bridge rails and transitions for pedestrian protection · barrier configuration to implement for...

Midwest States’ Regional Pooled Fund Research ProgramFiscal Year 1999-2000 (Year 10)

Research Project Number SPR-3(017)NDOR Sponsoring Agency Code RPFP-00-04

BRIDGE RAILS AND TRANSITIONS FOR

PEDESTRIAN PROTECTION

Submitted by

Nicholas R. Hiser, B.S.M.E., E.I.T.Graduate Research Assistant

Ronald K. Faller, Ph.D., P.E.Research Assistant Professor

Dean L. Sicking, Ph.D., P.E.Professor and MwRSF Director

John R. Rohde, Ph.D., P.E.Associate Professor

John D. Reid, Ph.D.Associate Professor

Karla A. Polivka, M.S.M.E., E.I.T.Research Associate Engineer

MIDWEST ROADSIDE SAFETY FACILITYUniversity of Nebraska-Lincoln

527 Nebraska HallLincoln, Nebraska 68588-0529

(402) 472-6864

Submitted to

MIDWEST STATE’S REGIONAL POOLED FUND PROGRAMNebraska Department of Roads

1500 Nebraska Highway 2Lincoln, Nebraska 68502

MwRSF Research Report No. TRP-03-127-03

February 20, 2003

Technical Report Documentation Page1. Report No. 2. 3. Recipient’s Accession No.

SPR-3(017)

4. Title and Subtitle 5. Report Date

Bridge Rails and Transitions for Pedestrian Protection February 20, 20036.

7. Author(s) 8. Performing Organization Report No.

Hiser, N.R., Faller, R.K. Sicking, D.L., Rohde, J.R., Reid,J.D., and Polivka, K.A.

TRP-03-127-03

9. Performing Organization Name and Address 10. Project/Task/Work Unit No.

Midwest Roadside Safety Facility (MwRSF)University of Nebraska-Lincoln527 Nebraska HallLincoln, NE 68588-0529

11. Contract © or Grant (G) No.

SPR-3(017)12. Sponsoring Organization Name and Address 13. Type of Report and Period Covered

Midwest States’ Regional Pooled Fund ProgramNebraska Department of Roads1500 Nebraska Highway 2Lincoln, Nebraska 68502

Final Report 1999-200314. Sponsoring Agency Code

RPFP-00-0415. Supplementary Notes

Prepared in cooperation with U.S. Department of Transportation, Federal Highway Administration16. Abstract (Limit: 200 words)

It is desirable to protect pedestrians on bridges from motor vehicles. However, transition problems arise at theends of bridges where the bridge rail, bridge rail end treatment, and pedestrian walkway compete for the limitedavailable space. The objective of this study was to identify the most common scenarios in which the protection ofpedestrians on bridges is desirable, and then to develop bridge rail and bridge rail end treatment configurations toaccommodate those situations. The objective was achieved by performing a field investigation, a survey of statetransportation agencies, and a literature review. Recommendations for the placement and general design of standardbarrier configurations have been provided in the form of thirteen generalized site drawings. The barrier configurationsoutlined within this report were based on NCHRP Report No. 350 approved hardware, roadside hardware meeting priorsafety standards, hardware believed to provide moderate safety, hardware currently under development, and soundengineering judgement. Therefore, the barrier configurations recommended herein are not equivalent in terms of thelevel of pedestrian safety provided. As a result, sound engineering judgement is required when determining whichbarrier configuration to implement for providing pedestrian protection on and near the ends of bridges.

17. Document Analysis/Descriptors 18. Availability Statement

Highway Safety, Roadside Safety, Bridge Railing,Approach Guardrail Transition, Longitudinal Barrier,Pedestrian Protection, Bicycle Protection

No restrictions. Document available from:National Technical Information Services,Springfield, Virginia 22161

19. Security Class (this report) 20. Security Class (this page) 21. No. of Pages 22. Price

Unclassified Unclassified 98

ii

DISCLAIMER STATEMENT

The contents of this report reflect the views of the authors who are responsible for the facts

and the accuracy of the data presented herein. The contents do not necessarily reflect the official

views or policies of the State Highway Departments participating in the Midwest States’ Regional

Pooled Fund Research Program nor the Federal Highway Administration. This report does not

constitute a standard, specification, or regulation.

iii

ACKNOWLEDGMENTS

The authors wish to acknowledge several sources that made a contribution to this project:

(1) the Midwest States’ Regional Pooled Fund Program funded by the Connecticut Department of

Transportation, Iowa Department of Transportation, Kansas Department of Transportation,

Minnesota Department of Transportation, Missouri Department of Transportation, Montana

Department of Transportation, Nebraska Department of Roads, Ohio Department of Transportation,

South Dakota Department of Transportation, Texas Department of Transportation, and Wisconsin

Department of Transportation for sponsoring this project; and (2) the University of Nebraska-

Lincoln for matching support.

A special thanks is also given to the following individuals who made a contribution to the

completion of this research project.

Midwest Roadside Safety Facility

R.W. Bielenberg, M.S.M.E., Research Associate EngineerJ.C. Holloway, M.S.C.E., Research Associate EngineerUndergraduate and Graduate Assistants

Iowa Department of Transportation

David Little, P.E., Assistant District EngineerWill Stein, Design Methods Engineer

Kansas Department of Transportation

Ronald Seitz, P.E., Assistant Bureau ChiefRodney Lacy, P.E., Road Design Leader

Missouri Department of Transportation

Daniel Smith, P.E., Research and Development EngineerDavid Silvestor, Design Standards EngineerTom Allen, Project Development Engineer

iv

Minnesota Department of Transportation

Erik Wolhowe, Structures Research EngineerJim Klessig, Implementation LiaisonMohammad Dehdashti, P.E., Design Standards EngineerAndrew Halverson, P.E., former Assistant Design Standards Engineer

Nebraska Department of Roads

Phil Tenhulzen, P.E., Design Standards EngineerMark Traynowicz, P.E., Assistant Engineer, Construction DivisionAmy Starr, Research EngineerLeona Kolbet, former Research Coordinator

Ohio Department of Transportation

Dean Focke, P.E., Roadway Standards EngineerMonique Evans, P.E., Administrator

South Dakota Department of Transportation

Bernie Clocksin, Lead Project Engineer

Texas Department of Transportation

Mark Bloschock, P.E., Supervising Design EngineerMark Marek, P.E., Design Engineer

Wisconsin Department of Transportation

Beth Cannestra, P.E., Chief Roadway Development EngineerPeter Amakobe, Standards Development Engineer

Montana Department of Transportation

Susan Sillick, Research Bureau Chief

Connecticut Department of Transportation

Dionysia Oliveira, Transportation Engineer 3

Federal Highway Administration

John Perry, P.E., Nebraska Division Office

v

TABLE OF CONTENTSPage

TECHNICAL REPORT DOCUMENTATION PAGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i

DISCLAIMER STATEMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii

ACKNOWLEDGMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

TABLE OF CONTENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vList of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viiiList of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x

1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1 Problem Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.3 Objective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.4 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2 LITERATURE REVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.2 Pedestrian and Bicycle Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.2.1 Pathway Guidance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.2.2 Separation Guidance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.3 Bridge Railings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.4 Bridge Railing End Treatments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.5 Curbs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102.6 Relevant Approved Hardware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2.6.1 Approach Guardrail Transition with Curb . . . . . . . . . . . . . . . . . . . . . . . . . 142.6.2 W-beam Guardrail Over Curbs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152.6.3 Combination Vehicle/Pedestrian and Combination Vehicle/Bicycle

Bridge Rails . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152.6.4 Low-Height Bridge Rails and Barriers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3 STATE STANDARDS, PRACTICES, AND SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . 183.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183.2 Iowa Department of Transportation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.2.1 Pedestrian and Bicycle Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183.2.2 Bridge Railings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183.2.3 Bridge Railing End Treatments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183.2.4 Curbs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193.2.5 Typical Pedestrian Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

vi

3.3 Kansas Department of Transportation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193.3.1 Pedestrian and Bicycle Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193.3.2 Bridge Railings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193.3.3 Bridge Railing End Treatments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223.3.4 Curbs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

3.4 Missouri Department of Transportation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223.4.1 Pedestrian and Bicycle Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223.4.2 Bridge Railings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233.4.3 Bridge Railing End Treatments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233.4.4 Curbs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

3.5 Minnesota Department of Transportation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253.5.1 Pedestrian and Bicycle Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253.5.2 Bridge Railings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263.5.3 Bridge Railing End Treatments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263.5.4 Curbs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

3.6 South Dakota Department of Transportation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263.6.1 Pedestrian and Bicycle Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273.6.2 Bridge Railings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273.6.3 Bridge Railing End Treatments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273.6.4 Curbs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273.6.5 Typical Pedestrian Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

3.7 Texas Department of Transportation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283.7.1 Pedestrian and Bicycle Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283.7.2 Bridge Railings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323.7.3 Bridge Railing End Treatments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333.7.4 Curbs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

4 FIELD INVESTIGATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354.2 No Barrier Separation - Unlimited Approach Length . . . . . . . . . . . . . . . . . . . . . . . . 35

4.2.1 Transitions, Guardrails, and Terminals . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354.3 No Barrier Separation - Limited Approach Length . . . . . . . . . . . . . . . . . . . . . . . . . . 37

4.3.1 Curbs and Buffer Zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374.4 Barrier Separation Provided - Unlimited Approach Length . . . . . . . . . . . . . . . . . . . 37

4.4.1 Crash Cushions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374.4.2 Sloped Concrete End Terminal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404.4.3 Transitions, Guardrails, and Terminals . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404.4.4 Transitions, Guardrails, and Crash Cushions . . . . . . . . . . . . . . . . . . . . . . . 45

4.5 Barrier Separation Provided - Limited Approach Length . . . . . . . . . . . . . . . . . . . . . 494.5.1 Sloped Concrete End Terminal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494.5.2 Short Radius Guardrail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

vii

5 BRIDGE RAIL END TREATMENT CONFIGURATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . 565.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 565.2 No Barrier Separation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

5.2.1 Curbs, Placebo Barriers, and Buffer Zones . . . . . . . . . . . . . . . . . . . . . . . . 585.2.2 Unlimited Approach Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

5.2.2.1 Transitions, Guardrails, and Terminals . . . . . . . . . . . . . . . . . . . . 615.2.2.2 Crash Cushions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 645.2.2.3 Evaluation - No Barrier Separation, Unlimited

Approach Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 645.2.3 Limited Approach Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

5.2.3.1 Crash Cushions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 665.2.3.2 Short Radius Guardrails . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 665.2.3.3 Evaluation - No Barrier Separation, Limited

Approach Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 685.3 Barrier Separation Provided . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

5.3.1 Unlimited Approach Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 705.3.1.1 Transitions, Guardrails, and Terminals . . . . . . . . . . . . . . . . . . . . 705.3.1.2 Crash Cushions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 765.3.1.3 Low-Height Barriers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 805.3.1.4 Evaluation - Barrier Separation Provided, Unlimited

Approach Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 835.3.2 Limited Approach Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

5.3.2.1 Crash Cushions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 845.3.2.2 Low-Height Barriers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 845.3.2.3 Short Radius Guardrails . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 855.3.2.4 Evaluation - Barrier Separation Provided, Limited

Approach Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

6 SUMMARY AND CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

7 RECOMMENDATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

8 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

viii

List of FiguresPage

1. Vehicle Bumper Trajectory Illustration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132. Typical Pedestrian Facility over Bridge, Iowa Department of Transportation . . . . . . . . . . . . 203. Typical Pedestrian Facility over Bridge, Iowa Department of Transportation . . . . . . . . . . . . 214. Urban bridge with sidewalk, design speed less than or equal to 35 mph (56 km/hr),

South Dakota DOT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295. Urban bridge with sidewalk, design speed 40 to 45 mph (64 to 72 km/hr),

South Dakota DOT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306. Urban bridge with sidewalk, design speed 40 to 45 mph (64 to 72 km/hr),

South Dakota DOT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317. No Barrier Separation - Unlimited Approach Length - Transitions, Guardrails,

and Terminals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368. No Barrier Separation - Limited Approach Length - Curbs and Buffer Zones . . . . . . . . . . . . 389. Barrier Separation Provided - Unlimited Approach Length - Crash Cushion . . . . . . . . . . . . . 3910. Barrier Separation Provided - Unlimited Approach Length - Sloped Concrete

End Terminal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4111. Barrier Separation Provided - Unlimited Approach Length - Transitions, Guardrails,

and Terminals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4212. Barrier Separation Provided - Unlimited Approach Length - Transitions, Guardrails,

and Terminals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4413. Barrier Separation Provided - Unlimited Approach Length - Transitions, Guardrails, and

Crash Cushions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4614. Barrier Separation Provided - Unlimited Approach Length - Transitions, Guardrails, and

Crash Cushions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4815. Barrier Separation Provided - Limited Approach Length - Sloped Concrete End

Terminal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5016. Barrier Separation Provided - Limited Approach Length - Short Radius Guardrail . . . . . . . 5117. Barrier Separation Provided - Limited Approach Length - Short Radius Guardrail . . . . . . . 5318. Barrier Separation Provided - Limited Approach Length - Short Radius Guardrail . . . . . . . 5419. Typical Raised Sidewalk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5920. No Barrier Separation - Unlimited Approach Length - Curbs, Placebo Barriers, and

Buffer Zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6221. No Barrier Separation - Unlimited Approach Length - Transitions, Guardrails, and

Terminals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6322. No Barrier Separation - Unlimited Approach Length - Crash Cushions . . . . . . . . . . . . . . . . 6523. No Barrier Separation - Limited Approach Length - Crash Cushions . . . . . . . . . . . . . . . . . 6724. No Barrier Separation - Limited Approach Length - Short Radius Guardrails . . . . . . . . . . . 6925. Barrier Separation Provided - Unlimited Approach Length - Transitions, Guardrails,

and Terminals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7226. Barrier Separation Provided - Unlimited Approach Length - Transitions, Guardrails,

and Terminals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

ix

27. Barrier Separation Provided - Unlimited Approach Length - Transitions, Guardrails,and Terminals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

28. Barrier Separation Provided - Unlimited Approach Length - Transitions, Guardrails,and Terminals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

29. Barrier Separation Provided - Unlimited Approach Length - Crash Cushions . . . . . . . . . . . 7730. Barrier Separation Provided - Unlimited Approach Length - Crash Cushions . . . . . . . . . . . 7831. Barrier Separation Provided - Unlimited Approach Length - Crash Cushions . . . . . . . . . . . 7932. Barrier Separation Provided - Unlimited Approach Length - Low Height Barriers . . . . . . . 8133. Barrier Separation Provided - Limited Approach Length - Crash Cushions . . . . . . . . . . . . . 8634. Barrier Separation Provided - Limited Approach Length - Low Height Barriers . . . . . . . . . 8735. Barrier Separation Provided - Limited Approach Length - Short Radius Guardrails . . . . . . 8836. Barrier Separation Provided - Limited Approach Length - Short Radius Guardrails . . . . . . 91

x

List of TablesPage

1. Table 4-09.3 from Missouri Department of Transportation Design Manual . . . . . . . . . . . . . . 24

1

1 INTRODUCTION

1.1 Problem Statement

Urban arterial streets in heavily populated areas often have bridges that carry large volumes

of both vehicular and pedestrian traffic. In these situations, it is desirable to protect the pedestrians

from motor vehicles by creating pedestrian facilities that are separated from the motor vehicle lanes.

However, transition problems arise at the ends of bridges where the bridge rail, bridge rail end

treatment, and pedestrian walkway compete for the limited available space. The configuration of

the bridge rail end treatment is further complicated by the geometry of the adjoining roadway or

other limiting features at the site, such as roadway drainage and curb usage. For these reasons,

roadway designers and engineers have a need for rational guidelines that address pedestrian

protection at the ends of bridges. Thus, two questions must be answered: (1) when and to what

degree should pedestrians be protected from traffic on bridges; and (2) how should the traffic

barriers and transitions be configured for the most common scenarios.

1.2 Background

With the public’s increased awareness of environmental concerns, energy efficiency, and

individual health benefits, pedestrian traffic is on the rise. As a result, roadway designers must often

consider the need for adequate separation between vehicles and pedestrians on roadways, and

specifically within the confined conditions on bridges. Bridge design objectives in the past have

primarily targeted the accommodation of vehicular traffic, and thus, vehicular bridges are often the

only alternatives for pedestrian traffic to cross over obstacles such as interstate highways, railroad

tracks, and waterways. When pedestrians and motor vehicles are forced to compete for space, it is

apparent that the safety of the pedestrian is inherently at risk. In order to provide for the safety of

2

the pedestrians on bridges, it is a critical concern to address the separation of these two distinctly

different types of traffic during the planning and design process. Currently, there is little in the way

of standards or guidelines concerning the various configurations of guardrails and transitions

suitable for pedestrian protection near the ends of bridges. The result is that engineers are faced with

assessing the site criteria and specifying pedestrian facilities on a case-by-case basis.

1.3 Objective

The first objective of the research project was to identify the most common scenarios in

which the protection of pedestrians on bridges is desirable, and then develop bridge rail and bridge

rail end treatment configurations to accommodate those situations. In the future, guidelines should

be generated to assist designers evaluating pedestrian safety concerns. In addition, a cost-

effectiveness or benefit-to-cost ratio approach should be utilized in order to evaluate potential safety

improvements when accommodating pedestrians on or near bridges, as well as to aid in the

implementation of those pedestrian facilities deemed necessary on bridges, especially near the bridge

ends.

1.4 Scope

This study focused on the completion of the first project objective, which included the

identification of the most common bridge scenarios that merit the accommodation of pedestrians,

as well as the development of the corresponding standard barrier configurations for those scenarios.

For this study, it was impractical and unnecessary to conduct full-scale vehicle crash tests for all of

the recommended barrier configurations that may be used to provide pedestrian protection. Instead,

the barrier configurations outlined within this report were based on several factors. First, when

possible, roadside safety hardware that was shown to be acceptable according to the current impact

3

safety standards provided in the National Cooperative Highway Research Program (NCHRP) Report

No. 350 (1) was utilized. Second, if NCHRP Report No. 350-approved hardware was unavailable,

then roadside hardware, which either meets prior safety standards, is believed to provide moderate

safety, or is currently under development, was considered for providing improved protection and

accommodation of pedestrians on or near bridges. Finally, where guidance was unavailable in the

literature, sound engineering judgement was also used to aid in the determination of the barrier

configurations provided herein. However, it should be noted that the barrier configurations

recommended herein are not equivalent in terms of the level of pedestrian safety provided. As a

result, the engineer and designer must use sound engineering judgement when determining which

barrier configuration to implement.

The first objective of this study was achieved by performing a field investigation, a survey

of state transportation agencies, and an extensive literature review. The field investigation and state

survey assisted in identifying the most common situations where pedestrian protection is desired.

The literature review focused on the many NCHRP Report No. 350 (1) crash tested bridge rails, the

various types of bridge rail end treatments, and the standards that pertain to the design of bridge

rails, pedestrian rails, sidewalks, curbs, and other pedestrian facilities. Once the field investigation,

state survey, and literature review were completed, the information was evaluated, organized, and

documented. Recommendations for the placement and configuration of standard barrier

configurations were then made in the form of generalized site drawings.

There is a need for design guidelines that would assist roadway and bridge engineers to

determine when pedestrian protection on bridges is warranted. It is currently believed that these

design guidelines will be developed as a part of NCHRP Project 22-12(2). The procedures used to

4

establish the guidelines will be based on a detailed Benefit/Cost analysis of the risk to pedestrians

associated with unshielded sidewalks on bridges. It is interesting to note that the risk to pedestrians

is only moderately higher on bridges than on any sidewalk placed close to a roadway. Hence, it is

recommended that protection of pedestrians adjacent to any roadway should be explored in a future

study.

5

2 LITERATURE REVIEW

2.1 Introduction

Many existing publications address the various aspects of pedestrian protection on bridges.

Relevant topics include specifications for both bridge and pedestrian railings, combination

vehicle/pedestrian railings, bridge railing end treatments, approach guardrail transitions, standard

guardrail, guardrail end terminals, curb geometry, sidewalk geometry, and various combinations

thereof. A brief summary of the currently available information relevant to the protection of

pedestrians on or near bridges is included in the following sections.

2.2 Pedestrian and Bicycle Facilities

Increased pedestrian and bicycle traffic has resulted in an increased demand for engineering

guidelines for use in specifying pedestrian and bicycle facilities. Historically, general guidance can

be found in several publications on the accommodation of pedestrians and bicyclists as they relate

to their corresponding pathways. A literature review summary on those pathways as well as on the

separation of pedestrians and vehicles is provided herein.

2.2.1 Pathway Guidance

Sidewalks, walkways, and shared use paths are often placed adjacent to roadways to

accommodate pedestrian traffic. As a result, engineers and designers must strive to maintain the

safety of the users when specifying the geometry of these pathways. According to A Policy on

Geometric Design of Highways and Streets (the Green Book), published by the American

Association of State Highway and Transportation Officials (AASHTO), walkway width may vary

from 1,220 to 2,440 mm, and an additional 610 mm of width should be added when the sidewalk

is placed adjacent to a curb (2). In cases where sidewalks are built adjacent to high-speed highways,

6

buffer zones should be incorporated to separate the pedestrian path from the traveled way for

additional pedestrian safety. The guidelines given previously can also be applied to pedestrian

accommodations on bridges. However, it is noted that due to unique bridge site features and higher

installation costs, pedestrian path details on bridges will often differ from those used along the

approach roadway (2). For example, AASHTO’s LRFD Bridge Design Specifications recommends

a 1,524 mm minimum width for a raised sidewalk on a bridge (3), which is 305 mm narrower than

the guidelines given in the Green Book.

AASHTO’s Guide for the Development of Bicycle Facilities (the Bicycle Guide) (4)

specifically addresses bicycle path width. It states that any facility designed for use by bicyclists

should have a minimum width of 1,220 mm. In locations with high traffic volumes, substantial truck

traffic, or vehicle speeds exceeding 80 km/hr, a bicycle path width of 1,524 mm is preferable and

additional width is desirable for the accommodation of bicycle traffic (4).

In addition to adequate pathway width and placement, maintaining continuity and

consistency of the pathway is important for the safe and efficient movement of pedestrians and

bicyclists, especially near bridge approaches (2,4). In general, sidewalks are inappropriate for the

accommodation of bicyclists, except for infrequent uses such as crossing long, narrow bridges.

Therefore, sidewalks should be reserved for primary use by pedestrians on foot (4,5). Both

pedestrian and bicycle paths should have a smooth surface and a 2 percent minimum cross slope in

order to provide for adequate water drainage. An adequate cross slope will minimize several safety

concerns such as water ponding, accumulation of debris, and ice formation (4). All walkways and

sidewalks must also be designed to accommodate the physically handicapped (2).

7

2.2.2 Separation Guidance

The most desirable method for protecting pedestrians and bicyclists is to separate them from

vehicular traffic (6). Separation can be defined as any method used to reduce or eliminate the

vehicular hazard to pedestrians and bicyclists. General separation techniques could include

horizontal distance, vertical grade, or physical barrier separation. However, it is a difficult task for

engineers to match an appropriate separation method with the required facility need due to the lack

of available objective guidance regarding pedestrian protection (6). Though desirable, lateral

separation over a distance or the use of grade separations are sometimes impractical solutions, and

thus, pedestrian and bicycle pathways are often placed adjacent to vehicular traffic lanes.

Because of the inherent differences between pedestrian and vehicular traffic, pedestrians are

at high risk from errant vehicles. In these cases, it is often desirable to specify protection for

pedestrians in the form of barrier separation. The Roadside Design Guide (RDG) (6), recommends

the use of a barrier curb to separate vehicles and pedestrians on low-speed roadways with speeds less

than 40 km/hr. Although no specific guidance is given, the use of other separation techniques are

recommended for roadways with speeds greater than 40 km/hr (6). In addition, the RDG states, “In

low-speed situations with the bridge railing at the outer edge of the sidewalk, a raised sidewalk may

provide some protection for pedestrians”(6). Where bridges are used to accommodate both vehicles

and pedestrians, separation is of prime concern due to the limited available width and fewer escape

routes for pedestrians. In these cases, separating vehicle and pedestrian lanes with a bridge railing

provides the maximum pedestrian protection (6). Specifically, on urban expressway bridges,

AASHTO’s Standard Specifications for Highway Bridges (7) recommends that pedestrian lanes

should be separated from vehicle lanes with combination vehicle/pedestrian bridge railings.

8

2.3 Bridge Railings

In addition to the available guidance concerning pedestrian and bicycle facilities, there also

exists engineering guidelines directed toward specifying bridge railings for pedestrian

accommodation and safety. For example, AASHTO’s LRFD Bridge Design Specifications

addresses a situation where a pedestrian pathway is placed between the vehicle lanes and the bridge

railing (3). It states that combination vehicle/pedestrian bridge railings, used in conjunction with

a raised sidewalk and a 152 to 203-mm tall curb, should only be used on low-speed highways with

posted speeds of 72 km/hr or less. AASHTO’s RDG states that the need for shielding of pedestrians

and bicyclists on bridges is based on several factors, such as traffic volumes and vehicle speeds, the

volume of pedestrian and bicycle traffic, and the geometrical conditions at the ends of the bridge (6).

However, the RDG provides no specific guidance as to when a pedestrian path should be protected

by a bridge railing system. In cases where a bridge railing is placed between vehicle lanes and the

sidewalk, a pedestrian railing is required on the outside edge of the pathway (6). AASHTO’s

Standard Specifications for Highway Bridges is somewhat more specific in its guidance as it

recommends the use of combination bridge railings to separate pedestrian and vehicle lanes on urban

expressway bridges, with additional pedestrian railings placed on the outside edge of the bridge (7).

Finally, AASHTO’s LRFD Bridge Design Specifications is even more specific in its guidance when

it recommends the shielding of pedestrian paths on high-speed roadways, with posted speeds of 80

km/hr or more, using combination bridge railings with additional pedestrian railings on the outside

edge of the pathway (3). On bridges, pedestrian-only railings should be a minimum of 1,067-mm

tall, bicycle railings should be a minimum of 1,372-mm tall, and combination railings should

conform to the respective pedestrian or bicycle railing requirements depending on the facility type

9

(3,7). AASHTO’s Bicycle Guide recommends a minimum railing height of 1,067 mm for both

bicycle railings and combination vehicle/bicycle railings (4), which is in contrast to the 1,372-mm

railing height specified in AASHTO’s Standard and LRFD Bridge Specifications (3,7).

2.4 Bridge Railing End Treatments

The ends of rigid concrete bridge railings provide a significant hazard to vehicles and their

occupants, and unfortunately, adequately shielding the ends of bridge rails often presents a

significant problem for engineers. Exposed bridge rail ends and sharp changes in railing geometry

should be avoided, and a smooth stiffness transition between the bridge rail and the adjoining barrier

system should be provided to prevent pocketing and snagging of an impacting vehicle (2, 7).

Various bridge rail end treatments or transitional barrier systems are available to protect traffic from

direct impact with the bridge rail ends. Incorporation of these transitional structures should not

impede pedestrian traffic if an adjacent walkway is present (2). It is required that the entire length

of need associated with the hazard or obstruction must be effectively shielded, either by the selected

bridge rail end treatment or the bridge rail itself (6). Other obstructions, such as intersecting

roadways, streets, and drives often make it difficult to adequately shield the ends of bridge railings

and/or provide the required length of need. AASHTO’s RDG states that the best solution is to

relocate the intersecting road and to install a standard bridge rail end treatment (6). When is it not

possible to use a standard bridge rail end treatment, other means should be used in an attempt to

shield the bridge rail end and the hazard located behind the bridge rail. However, it is noted that

using non-standard methods of terminating bridge railings often compromises the barrier’s ability

to effectively shield the hazards, and often results in some sacrifice in the crashworthiness of the

barrier (6).

10

2.5 Curbs

AASHTO’s Green Book defines two types of curbs: vertical curbs and sloping curbs (2).

Vertical curbs were originally designed to inhibit or discourage vehicles from leaving the roadway.

Vertical curbs are typically between 152 and 229-mm tall and are characterized by their tall, steep

faces. On the contrary, sloping curbs were designed to intentionally allow vehicles to mount and

cross over them. Sloping curbs are typically between 102 and 152-mm tall and have sloping, well

rounded faces (2).

Vertical curbs serve several purposes, such as discouraging vehicles from leaving the

roadway, delineating pedestrian walkways or pavement edge, and channeling water runoff (2).

According to Olsen et al, it has been shown that vertical curbs are inadequate for redirecting errant

vehicles that leave the roadway (8). As a result, the primary use of vertical curbs concerning

pedestrian protection is for delineation of the vehicle and pedestrian lanes. Although vertical curbs

will not provide shielding of the pedestrian facility, there is some positive effect on delineation as

they tend to discourage the mingling of the two distinctly different traffic types. State transportation

agencies, surveyed in the ongoing NCHRP study, Project 22-17 Recommended Guidelines for Curbs

and Curb-Barrier Combinations (9), identified drainage control as the primary or secondary reason

for specifying vertical curbs. Walkway support and pavement delineation were also highly rated.

AASHTO’s Green Book and RDG state that sloping curbs typically provide roadway

delineation and channelization of water runoff (2, 6). Although sloping curbs were originally

intended to be used in areas where pedestrian protection was not a concern, the failure of vertical

curbs to offer any significant protection has prompted some agencies to begin using sloping curb

designs adjacent to sidewalks. A state agency survey conducted within NCHRP Report 22-17

11

revealed that the primary functional purpose for using both vertical and sloping curbs is to provide

roadway drainage (9).

Both AASHTO’s Green Book and RDG state that neither vertical nor sloping curbs should

be used on freeways or high-speed roadways (2,6). The RDG recommends the use of vertical curbs

as a technique to separate vehicles and pedestrians only on low-speed roadways where speeds are

less than 40 km/hr (6). For roads with speeds greater than 40 km/hr, other safety provisions should

be made to shield pedestrians (6).

There are some conflicting views toward the use of curbs on bridges. AASHTO’s Standard

Specifications for Highway Bridges states that curb heights on bridges should be equal to or greater

than curb heights on the approach roadways (7). If there is no curb on the approach roadway, the

curb height on the bridge should be between 203 to 254 mm (7). AASHTO’s LRFD Bridge Design

Specifications recommends that the curb height for raised sidewalks on bridges should be a

maximum of 203 mm (3).

Currently, there is much concern and controversy regarding curbs used in conjunction with

roadside barriers. This fact is primarily due to the limited amount of data that is available. In 1974,

NCHRP published Report No. 150, Effect of Curb Geometry and Location on Vehicle Behavior,

which provided research results concerning the effect that various mountable and barrier curbs have

on the trajectory of an impacting vehicle (8). The crash test data revealed that vehicular impacts

with curbs can create post-impact trajectories that lead to vehicular vaulting of 686-mm high W-

beam guardrail when located behind the curb. Initial front-end dipping of the test vehicle was also

observed, subsequently revealing the potential for underride and snagging of the guardrail barrier.

An example illustration of a vehicle’s bumper trajectory after an impact with a curb is provided in

Figure 1.

12

AASHTO’s Green Book and AASHTO’s RDG both give limited guidance on curb/barrier

combinations (2,6). In general, vertical curbs and sloping curbs should not be used in conjunction

with traffic barriers because the curb may cause vehicular vaulting of the barrier. In locations where

it is not possible to eliminate a curb/barrier combination, the curb should either be located behind

the barrier or flush with the barrier face so the vehicle trajectory is not altered prior to impact with

the barrier (2,6). Also, the use of a curb no higher than 100 mm and/or stiffening of the guardrail

to reduce its deflection may help to maximize the crashworthiness of the curb/barrier combination

(6). If extensive use of a curb/barrier combination is planned, and if there is no crash test data from

a similar test to make an informed judgement, the curb/barrier combination should be verified with

the use of a full-scale vehicle crash test (6).

Effective drainage, while one of the most important features to consider in roadway design,

should be implemented in a manner that considers the effect it has on other roadside safety features

(6). Thus, curbs and other drainage features (i.e., raised inlets, curb inlets, ditches, or swales) must

be designed for both hydraulic efficiency and roadside safety (6). Swales, or drainage ditches, can

often be used in lieu of curbs to handle drainage concerns (9). However, engineers should use

caution when specifying drainage features to be placed in front of barriers, since those features can

lead to vehiclular instabilities that can adversely affect the crashworthiness of the barrier system (6).

Finally, due to the potential for vehicular vaulting of the guardrail, the slope between the driving

lane and the barrier should be no steeper than 10:1 (6).

13

Figure 1. Vehicle Bumper Trajectory Illustration (9).

14

NCHRP Report 22-17, Recommended Guidelines for Curbs and Curb-Barrier Combinations,

is an ongoing study that is investigating the consequences of combining curbs and traffic barriers

on roadways with vehicle speeds greater than 60 km/hr (9). This study will utilize computer

simulation, crash test data analysis, and full-scale crash testing to investigate vehicle behavior during

impacts with curb/barrier combinations. When completed, this study should yield some new insights

with which objective guidelines concerning curb/barrier combinations can be developed.

2.6 Relevant Approved Hardware

The following is a listing of roadside hardware configurations that have been crash tested

and approved for use according to the NCHRP Report No. 350 safety standards. These roadside

hardware configurations have been included herein because they are suitable for use in the safe

accommodation of pedestrians on or near the ends of bridges.

2.6.1 Approach Guardrail Transition with Curb

Historically, approach guardrail transitions have been used to provide a lateral stiffness

transition between the bridge rail and the attached guardrail system and to prevent vehicles from

impacting the blunt end of the bridge rail. However, when used in a pedestrian situation, the

approach guardrail transition system can also effectively shield the pedestrians behind the barrier.

For some bridge applications, there is also a need to carry the water runoff from the bridge

to a point beyond the end of the bridge railing. As a result, a curb system is often utilized below the

approach guardrail transition, and even the standard guardrail, in order to provide hydraulic

drainage. However, prior crash testing has shown that curbs placed in front of or below guardrail

systems can result in override of the barrier as well as vehicular instabilities (8). Therefore, the need

exists to have crashworthy approach guardrail transition designs that are acceptable for use with a

curb.

15

In 1998, the Midwest Roadside Safety Facility (MwRSF) developed and crash tested two

thrie beam approach guardrail transition systems that incorporated a 102-mm high by 178-mm wide

triangular shaped lip curb (10, 11). These two transition systems successfully met the Test Level

3 (TL-3) requirements specified in NCHRP Report No. 350.

2.6.2 W-beam Guardrail Over Curbs

Prior research has shown that the crashworthiness of a guardrail system can be compromised

when used in conjunction with or near curbs (8). However, two recent studies have shown

acceptable safety performance of W-beam guardrail systems placed over curbs according to the

TL-3 standards of NCHRP Report No. 350. In the first study, the Texas Transportation Institute

(TTI) successfully crash tested a G4(2W) W-beam guardrail system placed over a 100-mm high

asphalt curb according to the TL-3 criteria of NCHRP Report No. 350 (12). In the second study,

MwRSF conducted two separate crash tests on guardrail systems placed above a curb. In the first

test, a modified G4(1S) W-beam guardrail system, installed over a 102-mm high by 203-mm wide

triangular-shaped lip curb, was unsuccessfully crash tested according to the TL-3 criteria of NCHRP

Report No. 350 (13). In a follow-up crash test, a modified G4(1S) guardrail system with double

nested W-beam rails was placed over a 102-mm high by 203-mm wide triangular-shaped lip curb

and successfully crash tested according to the TL-3 criteria of NCHRP Report No. 350 (14).

2.6.3 Combination Vehicle/Pedestrian and Combination Vehicle/Bicycle Bridge Rails

In 1998, MwRSF successfully developed and crash tested a combination vehicle/bicycle

bridge rail according to Test Level 4 (TL-4) requirements of NCHRP Report No. 350 (15). This

combination bridge railing system incorporated a steel tubular bicycle railing which was attached

to the back-side face of a standard New Jersey safety shaped barrier. For this application, both the

16

vehicle and bicycle traffic were intended to be on the traffic-side face of the bridge railing system.

However, if this railing were used to separate the vehicle and bicycle lanes, additional consideration

would be necessary to insure that the back side of the railing were free of protruding posts that could

pose a hazard to the bicyclists.

TTI successfully developed and crash tested the BR27D and BR27C combination

vehicle/pedestrian bridge railings (16). Both railing designs were constructed and crash tested in

two configurations - mounted on a raised sidewalk and mounted flush with the bridge deck. The

BR27D railing was successfully tested according to the Performance Level 1 (PL-1) criteria found

in AASHTO’s Guide Specifications for Bridge Railings (17) and was later approved for use in

applications requiring NCHRP Report No. 350 TL-2 systems. The BR27C railing was successfully

tested according to PL-2 criteria found in AASHTO’s Guide Specifications for Bridge Railings (17)

and was later approved by FHWA’s crash testing equivalency rating for use in applications requiring

NCHRP Report No. 350 TL-4 systems.

Another combination vehicle/pedestrian bridge railing, the Texas Type C411, was

successfully developed and crash tested by TTI (18). The combination railing was constructed on

top of a raised sidewalk and was crash tested with both 2,000-kg (4409-lb) and 860-kg (1896-lb)

vehicles. The crash test results indicated that the railing was suitable for use on low-speed roads of

72 km/hr or less. The Texas Type C411 bridge railing was later approved by FHWA’s crash testing

equivalency rating for use in NCHRP Report No. 350 TL-2 applications.

Finally, the New England Transportation Consortium (NETC) successfully developed a

sidewalk-mounted, combination vehicle/pedestrian steel bridge railing system (19). The four-bar

steel railing was successfully tested according to TL-3 criteria of NCHRP Report No. 350.

17

2.6.4 Low-Height Bridge Rails and Barriers

For low-speed roadways and bridges, low-height barriers are installation options where site

restrictions prevent the use of conventional barriers. In some cases, it may be appropriate to use

low-height barriers for pedestrian protection. In 1992, TTI developed and crash tested a low-profile

portable concrete barrier and a corresponding sloped end treatment which was deemed acceptable

for use on low-speed roadways of 72 km/hr or less (20-22). In 2001, MwRSF successfully

developed and crash tested a low-profile bridge railing system according to the TL-2 criteria of

NCHRP Report No. 350 (23). A sloped-concrete end terminal, based on prior testing of TTI’s

terminal, was also developed for use with the MwRSF low-profile bridge railing. The University

of Florida also successfully developed and crash tested a low-profile work-zone barrier according

to the NCHRP Report No. 350 TL-2 criteria (24).

18

3 STATE STANDARDS, PRACTICES, AND SPECIFICATIONS

3.1 Introduction

A survey of the state highway agencies participating in the Midwest States’ Regional Pooled

Fund Program was conducted to identify current practices regarding pedestrian protection on

bridges. Each of the 11 states in the Pooled Fund Program was asked to submit relevant information

that pertains to guidance utilized by engineers when specifying pedestrian facilities on or near

bridges. Beneficial information included state derived standards and specifications, commonly

accepted design practices, region specific concerns, and other general knowledge that helped guide

the study. Below is a summary of the relevant information that was provided.

3.2 Iowa Department of Transportation

The Iowa Department of Transportation contributed the following general guidance which

pertains to the protection of pedestrians and bicyclists on and near the ends of bridges.

3.2.1 Pedestrian and Bicycle Facilities

• Barrier separation of pedestrian and traffic lanes is provided on all new projectsregardless of traffic speed and type.

• In situations where old bridges with limited available width are being refurbished for

pedestrian accommodation, a curbed and elevated sidewalk can be used fordelineation between vehicle and pedestrian lanes.

3.2.2 Bridge Railings

• No information on this topic was provided.

3.2.3 Bridge Railing End Treatments

• For state highways with a posted speed of 35 mph (56 km/hr) or greater, a concretebarrier with crashworthy end treatment (either guardrail or impact attenuator) is usedto separate vehicular and pedestrian lanes.

19

• For posted speeds under 35 mph (56 km/hr), a concrete barrier with a sloped concreteend treatment is used between vehicles and pedestrians.

3.2.4 Curbs


3.2.5 Typical Pedestrian Facilities

Figures 2 and 3 illustrate typical pedestrian facilities over bridges that are used by the Iowa

Department of Transportation.

3.3 Kansas Department of Transportation

The Kansas Department of Transportation (KDOT) contributed the following guidance

which pertains to the protection of pedestrians and bicyclists on and near the ends of bridges.


The following guidance that is relevant to pedestrian and bicycle facilities is documented in

the KDOT Design Manual, Volume III, Bridge Section, Section 3.2.10.3, Sidewalks (25).

• Sidewalks used on bridges should have a minimum clear width of 1,500 mm.

• Designated bikeways should have a minimum useable clear width of 2,450 mm.

• As a general rule, pedestrians and bicyclists should be separated.


The following guidance for bridge railings is documented in the KDOT Design Manual,

Volume III, Bridge Section, Section 3.2.10.2, Railings (25).

• “If the design of a (bridge) structure includes a sidewalk, a concrete barrier rail willbe used between the traveled way and the sidewalk.”

• “For design speeds less than or equal to 65 km/hr, the minimum height of theseparator railing above the sidewalk shall be 600 mm and the railing surface shall besmooth to avoid snag points for pedestrians or cyclists.”

20

Figure 2. Typical Pedestrian Facility over Bridge, Iowa Department of Transportation

21

Figure 3. Typical Pedestrian Facility over Bridge, Iowa Department of Transportation

22

• “For design speeds over 65 km/hr, or if a high volume of bike traffic is expected andthe risk involved if a cyclist would fall over the separator is great, use a minimumrailing height of 1,070 mm.”

• “The height of the railing on the outside edge of the sidewalk shall be a minimum of1,070 mm for pedestrians and a minimum of 1,370 mm for bicycles.”

• “Chain link fence on bridges over the Interstate in urban areas shall be 1,830 mmhigh. At other locations, chain link fence shall be 1,370 mm high.”



3.3.4 Curbs

The following guidance for curbs is documented in the KDOT Design Manual, Volume III,

Bridge Section, Section 3.2.10.1, Curbs (25).

• “Where curb and gutter sections are used on the roadway approach, a closed sectionof rail on the bridge should match that on the road curb, except it may exceed theroad curb height on the approach.”

• “Bridge curbs serve the purposes of drainage control and delineation of pedestrianwalkways.”

• “Curbs shall be designed in accordance with AASHTO Articles 2.2.5 and 3.14.2.”,which references AASHTO’s Standard Specifications for Highway Bridges (7).

• “Current KDOT policy is not to use brush curbs on bridges.”

3.4 Missouri Department of Transportation

The Missouri Department of Transportation (MoDOT) contributed the following guidance



The following guidance for pedestrian and bicycle facilities is documented in the MoDOT

Design Manual, Chapter IV, Detail Design, Section 4-09.26, Bicycle/Pedestrian Facilities (26).

23

• Pedestrian and/or bicyclist accommodations should be considered when “the routeprovides access across a natural or man-made barrier, i.e, bridges over rivers,roadways or railroads, or under access-controlled facilities and roadways.”

• “The design and installation of pedestrian and bicycle facilities is at the solediscretion of the director or designee. Documentation should be developed on allprojects to support the decision to provide or not provide pedestrian and/or bicycleaccommodations.”

• “The AASHTO publication Guide for the Development of Bicycle Facilities andFHWA-RD-92-073 Selecting Roadway Design Treatments to Accommodate Bicyclesprovide guidance for bicycle and multi-use facilities.”

• “Table 4-09.3 provides guidance on the application of bicycle/pedestrian facilitieswith respect to roadway classification.” Refer to Table 1.

• “When provided, sidewalks should have a minimum width of 5 ft (1.5 m). Theabsolute minimum sidewalk width allowed by ADA (Americans with DisabilitiesAct) guidelines is 3 ft (0.9 m).”

• “A sidewalk proposed within 2 ft (0.6 m) of a curb should be adjacent to the curb,a minimum of 6 ft (1.8 m) wide and located behind a barrier curb.”

• “A pedestrian grade separation should only be constructed when the need for the safemovement of pedestrians cannot be solved in some simpler and more economicalmanner.”




The following guidance relevant to bridge railing end treatments is documented in the

MoDOT Design Manual, Chapter IV, Detail Design, Section 4-09.7, Guardrail (26).

• “Approved crashworthy end terminals are provided on guardrail placed for bridgeend protection.”

• Approved crashworthy end terminals are defined as terminals that have successfullypassed NCHRP 350 test criteria and have been approved by the FHWA.

24

Table 1. Table 4-09.3 from Missouri Department of Transportation Design Manual (26)

25

• “All downstream ends on two-way roadways are provided with an approvedcrashworthy end terminal.”

• “The length of need and the flare rate of the guardrail shall be determined inaccordance with the procedures contained in Section 5.6.4 of the AASHTO RoadsideDesign Guide.”

• “Guardrail is not generally used to protect traffic from the ends of bridges carryinga crossroad or street over the through lanes in developed areas where speed controlsexist or sidewalks are provided.”

3.4.4 Curbs

The following guidance for curbs is documented in the MoDOT Design Manual, Chapter IV,

Detail Design, Section 4-09.3, Curbs (26).

• “Curbs, and curb and gutter, are used to channelize and guide traffic, to mark trafficlanes, to define medians for safety, to simplify handling drainage, and to reduce rightof way requirements.”

• “When curbs are constructed directly beneath guardrail the curb height will be 4 in

(102 mm).”

• “Curbs are designed and located so that they are not hazardous to traffic.”

• “ Barrier type curbs are used in conjunction with other parallel vertical elements suchas walls, bridge rails, adjacent to sidewalks, etc.”

• “Barrier type curbs are offset from the edge of traffic lanes by at least 1 ft (300 mm),except curbs adjacent to auxiliary lanes 12 ft (3.6 m). At least a 4 ft (1.2 m) curboffset is desirable for short curb sections and for islands.”

3.5 Minnesota Department of Transportation

The Minnesota Department of Transportation (MnDOT) contributed the following guidance



The following guidance relevant to pedestrian and bicycle facilities is documented in the

MnDOT Bridge Design Manual, Section 5-392.201 D, Bridge Sidewalks and Bikeways (27).

26

• “Bridge sidewalks of 1.8 meters minimum widths should be provided where justifiedby pedestrian traffic. If bicycle traffic is expected the width should be 2.4 metersminimum and 3.0 meters desirable.”

• “Sidwalks and bikeways shall have a minimum cross slope of 0.01 meters permeter.”


The following guidance relevant to bridge railings is documented in the MnDOT Bridge

Design Manual, Section 5-392.201 D, Bridge Sidewalks and Bikeways (27).

• “When the design speed on the street is over 60 km/hr a concrete barrier is requiredbetween the roadway and the sidewalk (or bikeway) and a pedestrian (or bikeway)railing is required on the outside.”

• “When a barrier is provided between the traffic lanes and the sidewalk, the bridgeslab shall normally be used for the walkway.”


The following guidance for bridge railing end treatments is documented in the MnDOT

Bridge Design Manual, Section 5-392.201 E, Protective Rails at Bridge Approaches (27).

• “The ends of bridge railings must be protected from being impacted (except on lowspeed roads such as city streets). For design speeds over 60 km/hr, a crash testedguardrail transition (normally plate beam guardrail) is required.”

3.5.4 Curbs

The following guidance relevant to curbs is documented in the MnDOT Bridge Design

Manual, Section 5-392.201 D, Bridge Sidewalks and Bikeways (27).

• “The curb height for sidewalks adjacent to the roadway (on bridges) is 200 mmminimum.”

3.6 South Dakota Department of Transportation

The South Dakota Department of Transportation (SDDOT) contributed the following

guidance which pertains to the protection of pedestrians and bicyclists on and near the ends of

27

bridges. Chapter 3 of the SDDOT Road Design Manual generally states that AASHTO’s Geometric

Design of Highways and Streets (the “Green Book”) is to be referenced for design standard guidance

when establishing project criteria, and when the SDDOT Road Design Manual does not provide

guidance in a particular design area (28).



SDDOT Road Design Manual, Chapter 3, Section 6-i, Traffic Needs, Pedestrian Traffic (28).

• “Reference to national standards will be necessary until South Dakota develops moredemand for state standards.”

• All new bridges that have sidewalks are required to have a concrete barrier betweenthe vehicular traffic and the sidewalk.

• AASHTO’s Guide for the Development of Bicycle Facilities is used as a general

guideline for bicycle and pedestrian accommodation.




• If the design speed is less than or equal to 35 mph (56 km/hr), a sloped concreteterminal is used to protect the end of the bridge rail.

• If the design speed is 40 to 45 mph (64 to 72 km/hr), a guardrail transition or impactattenuator is used to protect the bridge rail and/or median barrier ends.

3.6.4 Curbs

The following guidance for curb usage is documented in the SDDOT Road Design Manual,

Chapter 7, Cross Sections, Curbs (28).

• Curbs “generally serve one or more of several purposes: drainage control, pavementedge delineation, delineation of pedestrian walkways, and assistance in orderlyroadside development.”

28

• “In the interest of safety, curbs should be omitted on high-speed rural highwayswhen the same objective can be attained by other acceptable means.”

• “Barrier curbs usually are limited to urban areas for typical street sections, withspeeds fo 40 mph (60 km/hr) or less.”

• “Mountable curbs can be used at median edges to outline channelizing islands inintersection areas, with speeds greater than 40 mph (60 km/hr). They also may beused at the outer edge of a shoulder to control drainage, improve delineation, andreduce erosion.”

3.6.5 Typical Pedestrian Facilities

Figures 4 through 6 illustrate typical pedestrian facilities over bridges that are used by the

South Dakota Department of Transportation.

3.7 Texas Department of Transportation

The Texas Department of Transportation (TxDOT) contributed the following guidance which

pertains to the protection of pedestrians and bicyclists on and near the ends of bridges.



TxDOT Bridge Railing Manual, Chapter 5, Section 2, Bridge Railing for Pedestrians (29).

• “A vehicular bridge with a design speed of 45 mph (72 km/hr) or less is considereda low-speed facility, and it does not require a separator railing if pedestrians use it.”

• “A bridge with a design speed above 45 mph (72 km/hr) is a high-speed facility, andit must have a separator railing if pedestrians use it.”


TxDOT Bridge Railing Manual, Chapter 5, Section 4, ADA Requirements for Bridge Railing (29).

• “Bridges in excess of 200 feet (61 m) in length must have a 5-foot (1,525-mm)minimum-width sidewalk or must have passing areas every 200 feet (61 m)projecting from the side of the bridge. Handrails meeting ADA requirements are notrequired at the sides of pedestrian slopes, but a pedestrian or bicycle railing isrequired.”

29

Figure 4. Urban bridge with sidewalk, design speed less than or equal to 35 mph (56 km/hr), South Dakota DOT

30

Figure 5. Urban bridge with sidewalk, design speed 40 to 45 mph (64 to 72 km/hr), South Dakota DOT

31

Figure 6. Urban bridge with sidewalk, design speed 40 to 45 mph (64 to 72 km/hr), South Dakota DOT

32


TxDOT Roadway Design Manual, Chapter 2, Section 6, Sidewalks and Pedestrian Elements (30).

• “Sidewalks provide distinct separation of pedestrian and vehicles, serving to increasepedestrian safety as well as to enhance vehicular capacity.”

• “For pedestrian comfort, especially adjacent to high speed traffic, it is desirable toprovide a buffer space between the traveled way and the sidewalk. For curb andgutter sections, a buffer space of 3 ft (915 mm) or greater between the back of thecurb and the sidewalk is desirable.”

• “Sidewalks should be wide enough to accommodate the volume and type ofpedestrian traffic expected in the area.”

• “The minimum clear sidewalk width is 5 ft (1,525 mm).”

• “Where a sidewalk is placed immediately adjacent to the curb, a sidewalk width of6 ft (1830 mm) is desirable to allow additional space for street and highwayhardware and allow for the proximity of moving traffic.”

• “Sidewalk widths of 8 ft (2,440 mm) or more may be appropriate in commercialareas, along school routes, and other areas with concentrated pedestrian traffic.”


TxDOT Roadway Design Manual, Chapter 6, Section 4, Bicycle Facilities (30).

• “The AASHTO Guide for the Development of Bicycle Facilities is the guide forplanning, design, construction, maintenance, and operation of bicycle facilities.”


The following guidance for bridge railings is documented in the TxDOT Bridge Railing

Manual, Chapter 1, Section 3, Texas Policy on Bridge Railing (29).

• “Texas Bridge Railing must meet or exceed design strength specified in theAASHTO Standard Specifications for Highway Bridges.”

• “Texas bridge railing on new construction must meet FHWA crash-test criteria asspecified in NCHRP Report 350.”

33


Manual, Chapter 5, Section 2, Bridge Railing for Pedestrians (29).

• “Combination railing is designed for use on the outside of raised sidewalks when noseparator railing is used on a facility with design speeds of 45 mph (72 km/hr) orless. It is sometimes used, though not typically required, as a separator railingbetween traffic on a high- or low-speed facility and an at-grade sidewalk.”

• “Railing for pedestrian-only bridges in Texas must comply with the geometry andstrength requirements of current AASHTO Bridge Design Specifications.”


Manual, Chapter 5, Section 3, Bridge Railing for Bicyclists (29).

• “Texas has adopted the AASHTO Bridge Design Specifications requirement thatrailing of bridges that are designated for bicycle traffic should be a minimum of 54inches (1372 mm) high...”.


The following guidance for bridge railing end treatments is documented in the TxDOT

Bridge Railing Manual, Chapter 5, Section 2, Bridge Railing for Pedestrians (29).

• “When using a separator railing, attach a metal-beam guard fence and terminate itat the end of the roadway shoulder, letting pedestrians walk behind the guard fence.”

• “If needed, a crash cushion can be used to absorb railing end impact energy.”

The following guidance for bridge railing end treatments is documented in the TxDOT

Roadway Design Manual, Appendix A, Section 2, Barrier Need (30).

• “Where the prescribed length of the guardrail cannot be installed at a bridge end dueto an intervening access point such as an intersecting roadway or driveway, thelength of guardrail may be interrupted or reduced. Alternative treatments in thesesituations include wrapping the guardrail around the radius of the access location,terminating the guardrail prior to the access location with an appropriate endtreatment and continuing the guardrail beyond the access location if necessary orusing an alternate bridge end treatment.”

34

3.7.4 Curbs

The following guidance for curbs is documented in the TxDOT Bridge Railing Manual,

Chapter 5, Section 2, Bridge Railing for Pedestrians (29).

• “A curb will adversely affect the performance of a barrier terminal.”

The following guidance for curbs is documented in the TxDOT Roadway Design Manual,

Chapter 2, Section 6, Curb and Curb and Gutters (30).

• “Curb designs are classified as vertical or sloping. Vertical curbs are defined asthose having a vertical or nearly vertical traffic face 6 inches (152 mm) or higher.Vertical curbs are intended to discourage motorists from deliberately leaving theroadway. Sloping curbs are defined as those having a sloping traffic face 6 inches(152 mm) or less in height. Sloping curbs can be readily traversed by a motoristwhen necessary.”

• “Curbs are used primarily on frontage roads, crossroads, and low-speed streets inurban areas. They should not be used in connection with the through, high-speedtraffic lanes or ramp areas except at the outer edge of the shoulder where need fordrainage, in which case they should be of the sloping type.”

The following guidance for curbs is documented in the TxDOT Roadway Design Manual,

Appendix A, Section 4, Placement of Guardrail (30).

• “Guardrail placed in the vicinity of curbs should be blocked out so that the face ofcurb is located directly below or behind the face of rail.”

• “To preclude vaulting or impacting at an undesirable position by errant vehicles, careshould be exercised in selecting placement location of guardrail with respect to slopeconditions. Guardrail may be placed at any lateral location on a side slope only ifthe slope rate between the edge of the pavement and the face of the barrier is 1:10 orflatter.”

35

4 FIELD INVESTIGATION

4.1 Introduction

A field investigation was undertaken in order to locate sites that exhibit various methods of

providing pedestrian protection on bridges. The bridge sites that were identified in this field

investigation have been categorized by two main criteria. The first criteria deals with the presence

or absence of a physical barrier between the vehicle and pedestrian lanes. The second criteria deals

with the available approach length at the end of the bridge system. The term “unlimited approach

length” is used herein to describe the situation where there is effectively unlimited space at the end

of the bridge system. In this case, the designer has the freedom to choose which type of bridge rail

end treatment to specify. Conversely, the term “limited approach length” is used to describe those

situations where limited space at the end of the bridge system constrains the designer with regard

to which type of bridge rail end treatment will be used. Approach length is determined by geometric

site constraints and land use in the vicinity of the bridge. Examples of these site constraints include

the existence of intersecting roadways, streets, or driveways, utility poles, fire hydrants, or other pre-

existing roadside hardware at the site. Following is a summary of relevant field sites that were

investigated.

4.2 No Barrier Separation - Unlimited Approach Length

4.2.1 Transitions, Guardrails, and Terminals

The bridge site shown in Figure 7 has no barrier separation and unlimited approach length.

The bridge railing, which is placed on the outer edge of the sidewalk, is a combination railing for

containment of both vehicular and pedestrian/bicycle traffic. The end of the bridge railing is

protected by a W-beam approach guardrail transition system, a length of W-beam guardrail, and an

36

Figure 7. No Barrier Separation - Unlimited Approach Length - Transitions, Guardrails, and Terminals

37

energy-absorbing guardrail end terminal. The sidewalk is raised relative to the bridge deck and

incorporates a curb and gutter between the sidewalk and traffic lanes. A mountable curb is used

adjacent to the sidewalk on the bridge approach, and a steep faced barrier curb is used on the bridge

itself. In both cases, the curb is intended to delineate the sidewalk and traffic lanes, as well as to

facilitate roadway drainage.

4.3 No Barrier Separation - Limited Approach Length

4.3.1 Curbs and Buffer Zones

The bridge site shown in Figure 8 has no barrier separation and limited approach length.

This particular site utilizes a curb and buffer zone to separate and delineate 88 km/hr traffic lanes

and the pedestrian walkway. The bridge railing, which is placed on the outer edge of the sidewalk,

is a combination railing for containment of both vehicular and pedestrian/bicycle traffic. Due to the

extremely limited approach length at this site, the bridge railing end is not protected with an end

treatment. The 3,050-mm wide sidewalk is directly adjacent to the bridge railing. A buffer zone,

comprised of textured, architectural pavement, is then located adjacent to the sidewalk and on the

traffic side. The buffer zone and sidewalk are both raised relative to the bridge deck by a barrier

curb. The barrier curb is intended to delineate the edge of the vehicular traffic lanes. The textured

pavement in the buffer zone is intended to discourage pedestrian use and increase the horizontal

separation distance between vehicles and pedestrians.

4.4 Barrier Separation Provided - Unlimited Approach Length

4.4.1 Crash Cushions

The bridge site shown in Figure 9 has barrier separation and unlimited approach length. The

bridge rail is a New Jersey-shape concrete barrier with an attached pedestrian/bicycle railing along

38

Figure 8. No Barrier Separation - Limited Approach Length - Curbs and Buffer Zones

39

Figure 9. Barrier Separation Provided - Unlimited Approach Length - Crash Cushions

40

the top edge. A pedestrian/bicycle railing is located on the opposite side of the sidewalk and on the

outermost edge of the bridge. The bridge rail end is protected by an energy-absorbing crash cushion,

which in this case is damaged. The sidewalk shifts laterally away from the roadway and the crash

cushion near the bridge end. The approach sidewalk is elevated by a mountable curb, which

terminates just upstream of the end of the crash cushion. The crash cushion is mounted flush with

the roadway, and the sidewalk adjacent to the crash cushion tapers gradually to the base of the crash

cushion. This configuration places the gutter line at the base of the crash cushion without the use

of a curb, and it keeps water from draining onto the sidewalk. Note that even though there is

unlimited approach length, the crash cushion does not appear to provide adequate length-of-need

to protect traffic from the drop-off hazard behind the bridge rail.

4.4.2 Sloped Concrete End Terminal

The bridge site shown in Figure 10 has barrier separation and unlimited approach length.

The bridge rail is a New Jersey-shaped concrete barrier which has a pedestrian/bicycle railing along

the top edge. There is a second pedestrian/bicycle railing located on the opposite side of the

sidewalk. The concrete barrier is terminated with a sloped-concrete end treatment that transitions

smoothly to the mountable curb that exists on the approach roadway. The sidewalk behind the

barrier shifts away from the roadway in order to increase the horizontal separation distance between

traffic and pedestrians at the end of the bridge. Again, even though there are no site restrictions, the

barrier that is used to separate pedestrians and traffic does not appear to provide adequate length-of-

need to shield the drop-off hazard behind the barrier.

4.4.3 Transitions, Guardrails, and Terminals

The first bridge site, as shown in Figure 11, has barrier separation and unlimited approach

41

Figure 10. Barrier Separation Provided - Unlimited Approach Length - Sloped Concrete End Terminal

42

Figure 11. Barrier Separation Provided - Unlimited Approach Length - Transitions, Guardrails, and Terminals

43

length. A vertical concrete parapet is used to separate the pedestrian sidewalk from the 64 km/hr

vehicle lanes, and a pedestrian/bicycle railing is placed along the top edge. At the end of the bridge,

the sidewalk shifts laterally away from the roadway to increase the distance separating the traffic

types, as well as to move the pedestrians clear of the flared guardrail and guardrail end terminal.

The bridge rail end is protected by a thrie beam approach guardrail transition and a flared W-beam

guardrail which is terminated using a guardrail end treatment. Present on the approach roadway is

a mountable S-shaped curb which transitions to a triangular-shaped lip curb upstream from the

guardrail end terminal. The lip curb is present beneath the guardrail and approach guardrail

transition until its junction with the base of the bridge rail. The elevation of the sidewalk tapers to

the level of the bridge deck over the length of the approach guardrail transition. The lip curb,

positioned under the approach guardrail transition, tapers back to the grade of the bridge deck

located behind the approach guardrail transition, thus forming a dike to prevent water runoff from

flowing onto the sidewalk. Although this design appears to provide adequate length-of-need to

protect motorists from the drop-off hazard behind the bridge rail, the guardrail posts are set in

concrete. Crash testing has shown that setting guardrail posts in concrete reduces the redirective

capacity of the barrier, and this practice should be avoided if possible.

The second bridge site, as shown in Figure 12, has barrier separation and unlimited approach

length. The bridge rail is a vertical concrete parapet which has a pedestrian/bicycle railing along

the top edge. A second pedestrian/bicycle railing is located on the opposite side of the sidewalk and

on the outermost edge of the bridge. The bridge rail end is protected by a thrie beam approach

guardrail transition and a flared W-beam guardrail which is terminated using a guardrail end

treatment. At the end of the bridge, the sidewalk shifts laterally away from the roadway to increase

44


45

the distance separating the traffic types, as well as to move the pedestrians clear of the flared

guardrail and guardrail end terminal. Present on the approach roadway is a mountable S-shaped

curb which transitions to a rounded lip curb at the junction of the W-beam to thrie beam transition.

The entire length of the W-beam guardrail and guardrail end terminal are placed on top of and

behind the mountable S-shaped curb. In addition, cutouts are provided in the sidewalk to allow the

guardrail posts to rotate in the soil and maintain the barrier’s redirective capacity.

In both Figures 11 and 12, the bridge rail ends are protected by thrie beam approach guardrail

transitions and flared W-beam guardrails which are terminated with guardrail end treatments.

However, there are some significant differences in curb placement that must be noted. The

mountable S-shaped curb on the approach roadway in Figure 11 transitions to a triangular-shaped

lip curb upstream of the guardrail end terminal in order to maintain drainage capacity, while

minimizing the effects on the trajectory of an impacting vehicle. Alternately, the configuration

shown in Figure 12, transitions from a mountable S-shaped curb to a rounded lip curb at the junction

of the W-beam to thrie beam transition, thus placing the guardrail and guardrail end terminal

systems directly behind the mountable S-shaped curb on the approach roadway. However, past

research has shown that the crashworthiness of a guardrail system may be affected by a curb located

beneath and/or in front of a barrier system (8). Therefore, it is concluded that the sites shown in

Figures 11 and 12 are not equivalent in terms of crashworthiness.

4.4.4 Transitions, Guardrails, and Crash Cushions

The first bridge site incorporating an approach guardrail transition with a crash cushion for

pedestrian protection, as shown in Figure 13, has barrier separation and unlimited approach length.

A New Jersey-shaped concrete barrier is used to separate the pedestrian sidewalk from the 56 km/hr

46

Figure 13. Barrier Separation Provided - Unlimited Approach Length - Transitions, Guardrails, and Crash Cushions

47

vehicle lanes, and a pedestrian/bicycle railing is placed along the top edge. A second

pedestrian/bicycle railing is located on the opposite side of the sidewalk and on the outermost edge

of the bridge. The end of the bridge rail is protected with an approach guardrail transition, standard

guardrail, and a Crash-Cushion Attenuating Terminal (CAT). The CAT is capable of providing

redirection for oblique impacts, as well as absorbing energy in end-on impacts. Present on the

approach roadway is a mountable S-shaped curb that transitions to a triangular-shaped lip curb at

the junction of the W-beam to thrie beam transition. At the end of the bridge, the sidewalk shifts

laterally away from the roadway to increase the distance separating the traffic types, as well as to

move pedestrians away from the CAT system.

The second bridge site, as shown in Figure 14, has barrier separation and unlimited approach

length. A New Jersey-shape concrete barrier is used to separate the pedestrian sidewalk from the

56 km/hr vehicle lanes, and a pedestrian/bicycle railing is placed along the top edge. A second

pedestrian/bicycle railing is located on the opposite side of the sidewalk and on the outermost edge

of the bridge. The end of the bridge rail is protected with an approach guardrail transition, standard

guardrail, and a CAT system. Present on the approach roadway is a mountable S-shaped curb that

remains present beneath the approach guardrail transition, standard guardrail, and CAT system until

its junction with the base of the bridge railing. At the end of the bridge, the sidewalk shifts laterally

away from the roadway to increase the distance separating the traffic types and also to move

pedestrians away from the CAT system.

Both Figures 13 and 14 display sites that utilize CAT systems to protect the bridge rail ends.

As before, there are some significant differences in curb placement must be noted. The curb on the

approach roadway in Figure 13 transitions to a triangular-shaped lip curb at the junction of the

48

Figure 14. Barrier Separation Provided - Unlimited Approach Length - Transitions, Guardrails, and Crash Cushions

49

W-beam to thrie beam transition. The full height of the S-shaped curb along the approach roadway

is maintained under the transition section shown in Figure 14. The CAT systems in both cases are

placed on top of and behind the mountable S-shaped curb on the approach roadway. However, past

research has shown that the crashworthiness of a guardrail system may be affected by a curb located

beneath and/or in front of a barrier system (8). Therefore, it is concluded that the sites shown in

Figures 13 and 14 are not equivalent in terms of crashworthiness.

4.5 Barrier Separation Provided - Limited Approach Length

4.5.1 Sloped Concrete End Terminal

The bridge site shown in Figure 15 has a barrier separating pedestrians and 72 km/hr traffic

lanes with an extremely limited approach length. The concrete bridge rail is a New Jersey-shaped

barrier with a pedestrian railing mounted along the top edge. A second pedestrian/bicycle railing

is located on the opposite side of the sidewalk and on the outermost edge of the bridge. The end of

the bridge rail is protected by a sloped concrete end terminal which tapers and transitions with the

curb line directly upstream of the bridge railing. The pedestrian sidewalk is raised relative to the

bridge deck. This design does not appear to provide adequate length-of-need to protect traffic from

the drop-off hazard behind the bridge rail.

4.5.2 Short Radius Guardrail

The first bridge site utilizing short radius guardrail, as shown in Figure 16, has a barrier

separating pedestrians and 64 km/hr traffic lanes, along with limited approach length due to its close

proximity to an intersecting street. The bridge rail is a vertical concrete parapet with a

pedestrian/bicycle railing along the top edge. A second pedestrian/bicycle railing is located on the

opposite side of the sidewalk and on the outermost edge of the bridge. A short radius guardrail

50

Figure 15. Barrier Separation Provided - Limited Approach Length - Sloped Concrete End Terminal

51

Figure 16. Barrier Separation Provided - Limited Approach Length - Short Radius Guardrail

52

system is used to shield the bridge rail end, to protect the pedestrians on the sidewalk, and to aid in

shielding the obstacle behind the bridge rail. A thrie beam approach guardrail transition is used

between the concrete bridge railing and the W-beam guardrail section of the short radius guardrail.

The W-beam guardrail turns the corner and terminates adjacent to the intersecting roadway. The

pedestrian sidewalk follows along the backside of the guardrail system and beyond the terminal end.

At this location, a pedestrian crosswalk is provided which traverses the roadway. Because the

sidewalk is at grade with the bridge deck, a concrete dike is located under the approach guardrail

transition and short radius guardrail systems in order to divert water runoff away from the sidewalk.

The second bridge site, as shown in Figure 17, has barrier separation between pedestrians

and 56 km/hr traffic lanes, along with limited approach length. A short radius guardrail system,

similar to site no. 1, is used to shield the bridge rail end, to protect the pedestrians on the sidewalk,

and to aid in shielding the obstacle behind the bridge rail. Unlike site no. 1, a mountable S-shaped

curb is installed flush with the face of the W-beam guardrail and transitions to a triangular-shaped

lip curb under the thrie beam transition section.

The third and final bridge site, as shown in Figure 18, has barrier separation between

pedestrians and vehicular traffic lanes, along with limited approach length. A short radius guardrail

system, similar to site nos. 1 and 2, is used to shield the bridge rail end, to protect the pedestrians

on the sidewalk, and to aid in shielding the obstacle behind the bridge rail. Unlike site nos. 1 and

2, the bridge rail does not have a pedestrian/bicycle railing along the top edge. This system is

mounted flush with the roadway, and no curbs are present on the bridge approach nor along the

approaching roadway.

53


54


55

The three short radius guardrail sites, as shown in Figures 16 through 18, appear to be very

similar in their design intent and construction. However, there are some significant differences in

curb placement that must be noted. Site no. 2, as illustrated in Figure 17, has a curb flush with the

face of the short radius guardrail system, while site no. 3, as shown in Figure 18, does not have a

curb present at all. Past research has shown that the crashworthiness of a guardrail system may be

affected by a curb located beneath or in front of a barrier system (8). Therefore, it is concluded that

the sites shown in Figures 17 and 18 are not equivalent in terms of crashworthiness.

It is also worthy to note that differences exist in hydraulic drainage capability at all three

sites. Site no. 1, as shown in Figure 16, has the pedestrian walkway placed at the grade of the bridge

deck. A variable height concrete dike is placed between the sidewalk and the vehicle lanes to

prevent roadway water runoff from draining across the sidewalk. The sidewalk at site no. 2, as

shown in Figure 17, is elevated relative to the bridge deck surface. This change in grade prevents

roadway water runoff from draining across the sidewalk. Finally, site no. 3, as shown in Figure 18,

incorporates no measures to keep roadway water runoff from draining across the sidewalk. Because

roadway drainage can contribute to water ponding, debris accumulation, and ice formation on the

pedestrian walkway, it is concluded that these three sites are not equivalent in terms of pedestrian

safety.

56

5 BRIDGE RAIL END TREATMENT CONFIGURATIONS

5.1 Introduction

The research previously conducted has helped to identify the most common scenarios in

which the protection of pedestrians on bridges is desirable. It has also defined the range of problems

and conditions that must be addressed within this study. The recommended solutions outlined herein

have been categorized by two main criteria. The first criteria deals with the presence or absence of

a physical barrier between the vehicle and pedestrian lanes. The second criteria deals with the

available approach length at the end of the bridge system.

Combination vehicle/pedestrian and vehicle/bicycle railings are used on bridges which carry

both vehicular and pedestrian/bicycle traffic and are designed to provide redirection capabilities and

containment for the vehicles traversing the bridge. These combination railings are commonly

incorporated into the bridge design using two basic configurations. For the first configuration, these

combination railings are installed at the outermost edge of the bridge structure. In these cases, the

pedestrian and bicycle pathways are located directly adjacent to the vehicle lanes and are often

placed on a raised sidewalk located on the traffic-side face of the bridge railing. Throughout this

report, this situation will be referred to as “no barrier separation.” For the second configuration,

these combination railings are placed between the vehicle and pedestrian/bicycle lanes in order to

shield the pedestrians and bicyclists from errant vehicles that may leave the traveled way. In these

cases, a second pedestrian/bicycle railing must be located on the opposite side of the pathway and

along the edge of the bridge structure. Within this report, this situation will be referred to as “barrier

separation provided.” However, if barrier separation is provided between the vehicle and bicycle

lanes, additional consideration should be given to ensure that the back side of the combination

57

railing is free from protruding posts that may pose a snagging hazard to bicyclists.

The term “unlimited approach length” is used herein to describe the situation where there

is effectively unlimited space at the end of the bridge system, thus allowing the designer the freedom

to choose which type of bridge rail end treatment will be implemented. And conversely, the term

“limited approach length” is used to describe those situations where limited space at the end of the

bridge system constrains the designer with regard to which type of bridge rail end treatment can be

installed. Approach length is determined by geometric site constraints and land use in the vicinity

of the bridge. Examples of these site constraints might include the existence of intersecting

roadways, streets, or driveways, utility poles, fire hydrants, or other pre-existing roadside hardware.

It is noted that situations with limited approach length must not compromise the length of need

required for the proper placement of the safety barrier. The length of need is defined in the

AASHTO’s Roadside Design Guide (6) as the length of barrier required to fully protect the hazard

located behind the barrier.

Within this chapter, the bridge rail end treatment configurations have been separated into

two main categories: “No Barrier Separation” and “Barrier Separation Provided”. These two main

categories have been further divided according to the site constraints: “Unlimited Approach Length”

and “Limited Approach Length”. Within each of these categories, configurations for treating bridge

rail ends have been detailed according to a specific roadside hardware type, such as crash cushions

or short radius guardrails.

5.2 No Barrier Separation

In some situations, adequate pedestrian safety can be provided on bridges by creating a

walkway that is adjacent to the vehicle traffic lanes without the use of a physical barrier. An

58

example of a combination vehicle/pedestrian railing placed on an elevated sidewalk is shown in

Figure 19. AASHTO’s LRFD Bridge Design Specifications recommends the use of a combination

vehicle/pedestrian railing adjacent to a raised sidewalk on roadways designed for 72 km/hr or less

(3). However, it is worthy to note that curbs are generally incapable of shielding the pedestrians

traversing elevated sidewalks on bridges, but rather curbs provide delineation between the sidewalk

and the traveled way discouraging the mingling of the traffic types. Furthermore, past research has

shown that the crashworthiness of a guardrail system may be affected by a curb located beneath

and/or in front of a barrier system (8).

Refer to Sections 2.2.2, 2.3, and 2.5 for a comprehensive summary of the current existing

guidelines concerning the protection of pedestrians using barrier separation.

5.2.1 Curbs, Placebo Barriers, and Buffer Zones

One major aspect of this study focused on curbs used in conjunction with bridge rail end

treatments. To date, there have been no published crash testing efforts performed on guardrail

terminals and crash cushions installed over curbs according to the NCHRP Report No. 350 safety

standards. Also, there has been very limited successful testing of approach guardrail transitions and

guardrail systems installed over curbs (10-14). As such, this study makes recommendations on curb

configurations and their placement relative to crashworthy roadside safety hardware based on the

following considerations:

(1) the use of curb/barrier configurations evaluated according to the NCHRP Report No.350 safety standards;

(2) the use of curb/barrier configurations that minimize the potential for safety concernsbased on prior research and sound engineering judgement; and

(3) the use of curb/barrier configurations that historically have been shown to provideadequate safety performance in the field.

59

Figure 19. Typical Raised Sidewalk with Combination Vehicle/Pedestrian Bridge Railing (3, 16)

60

The general cases illustrated herein take into consideration the fact that curbs are present on

the approaching roadways for controlling drainage or for other purposes. If curbs are not present

or drainage is handled in an alternative manner, it is assumed that crashworthy roadside hardware,

at the test level of the roadway in question, is placed at the end of the bridge railing and that the

pedestrians and bicyclists have been appropriately accommodated.

The results of NCHRP Report No. 150, The Effect of Curb Geometry and Location on

Vehicle Behavior (8), were previously noted and are reiterated here for clarity. The potential for

vehicular vaulting and/or snagging of barriers following an impact with curbs was demonstrated

under various speeds and impact conditions. The possible trajectory of a vehicle’s bumper with

respect to a guardrail system placed adjacent to or behind a curb following a vehicular impact with

a curb is illustrated in Figure 1(9). In general, prior research has shown that roadside barriers may

perform inadequately when placed over the top of curbs, and curbs used for delineation do not have

the ability to adequately redirect an errant vehicle. As a result, the physical protection of pedestrians

and bicyclists on bridges, as well as near the bridge approach, may be compromised due to the

presence of curbs (8).

A curb is sometimes called a placebo barrier because curbs, even barrier curbs, are

inadequate for preventing a vehicle from leaving the roadway (2). A buffer zone is simply a region

of lateral space placed between the vehicle lanes and the walkway. A curb and buffer zone

combination can also be placed between the vehicle and pedestrian lanes in order to clearly delineate

the separation of lane types as well as to provide increased recovery distance for the drivers of errant

vehicles. Both buffer zones and placebo barriers are intended to not only improve the safety of the

pedestrian but to also increase the pedestrian’s perceived level of safety. A typical example of the

61

use of curbs, placebo barriers, and buffer zones placed on a bridge and with unlimited approach

length is provided in Figure 20. Curbs, placebos, and buffer zones may be beneficial when used in

conjunction with other bridge rail end treatments, as well as in situations with limited approach

length.

5.2.2 Unlimited Approach Length

The ideal case for designers is a bridge site with ample approach length and lateral width to

accommodate both vehicular traffic and pedestrian/bicycle safety features. In this situation,

designers can freely specify appropriate pedestrian/bicycle safety facilities as well as bridge railing

end treatments without being forced to make compromises based on geometrical site constraints.

5.2.2.1 Transitions, Guardrails, and Terminals

A scenario with no barrier separation and unlimited approach length is illustrated in Figure

21. The ends of the bridge railing can be protected with either a TL-2, TL-3, or TL-4 approach

guardrail transition, strong-post guardrail, and guardrail end terminal. As shown in Figure 21, the

pedestrians and/or bicyclists are placed on pathways located on the traffic-side face of both the

bridge rail and guardrail systems, and a curb is placed at the edge of the traveled way.

For this scenario, two key points need to be addressed. First, in this situation, the pedestrians

and bicyclists positioned on the pathway are inherently at greater risk than if they were located

behind the barrier systems. This is due to the fact that they remain closer to the traveled way and

are unshielded from errant vehicles leaving the roadway. Therefore, research engineers as well as

bridge and roadway engineers must determine what increased levels of safety can be achieved when

separation is provided between the motorists and pedestrians. Most likely, a benefit-to-cost ratio

or cost-effectiveness analysis will be required in order to make this determination.

62

Figure 20. No Barrier Separation - Unlimited Approach Length - Curbs, Placebo Barriers, and Buffer Zones

63

Figure 21. No Barrier Separation - Unlimited Approach Length - Transitions, Guardrails, and Terminals

64

Second, past research has shown that curbs placed in front of or below guardrail systems may

result in vaulting or underride of the barrier as well as vehicular instabilities. Therefore, bridge and

roadway engineers should review the standard of practice on curb/barrier combinations and proceed

with caution when implementing their use in pedestrian facilities located on or near bridges.

However, it should also be noted that future research is required in order to determine the

appropriate placement of curbs relative to bridge rails, approach guardrail transitions, guardrails,

guardrail terminals, and crash cushions.

5.2.2.2 Crash Cushions

A second scenario with no barrier separation and unlimited approach length is illustrated in

Figure 22. In this case, the bridge rail ends are protected with either a TL-2 or TL-3 energy-

absorbing crash cushion. As shown in Figure 22, the pedestrian and/or bicyclist pathways are

located on the traffic-side face of both the bridge rail and crash cushion systems, and a curb is placed

at the edge of the traveled way. Additional discussion on the positioning of the pathways and the

curbs is the same as that provided in Section 5.2.2.1.

5.2.2.3 Evaluation - No Barrier Separation, Unlimited Approach Length

Three methods for providing pedestrian protection on bridges where there exists unlimited

approach length at the site and barrier separation is not provided have been illustrated in Figures 20

through 22. The roadside hardware utilized at all three sites is equivalent in terms of basic

crashworthiness since all hardware has been crash tested according to the NCHRP Report No. 350

impact safety standards. However, it must be noted that placement of these barriers relative to curbs

greatly affects crashworthiness due to the potential for vehicular vaulting of the barrier under certain

impact conditions. Therefore, further research is required in order to determine the appropriate, safe

65

Figure 22. No Barrier Separation - Unlimited Approach Length - Crash Cushions

66

placement of curbs in these situations. In cases where additional buffer zone width is used to

increase lateral separation between the pedestrian walkway and traffic lanes, Figure 20 may provide

the highest level of safety to pedestrians. Increased buffer zone width may also help to stabilize the

vehicle prior to impact with the barrier, thus improving the crashworthiness of the barrier when

located behind the curb.

5.2.3 Limited Approach Length

Bridge sites with limited approach length will not allow the use of conventional approach

guardrail transitions, standard guardrail, and guardrail end terminals. In these situations, the

designer is forced to specify alternative bridge rail end treatments that appropriately satisfy the

safety requirements of the site.


A scenario that has no barrier separation and limited approach length is illustrated in Figure

23. In this case, the bridge rail ends are protected with either a TL-2 or TL-3 energy-absorbing crash

cushion. A crash cushion is used in place of typical approach guardrail transitions, standard

guardrails, and guardrail end terminals due to the close proximity of an intersecting roadway, street,

or driveway on the approach side of the bridge. As shown in Figure 23, the pedestrian and/or

bicyclist pathways are located on the traffic-side face of both the bridge rail and crash cushion

systems, and a curb is placed at the edge of the traveled way. Additional discussion on the

positioning of the pathways and the curbs is the same as that provided in Section 5.2.2.1.

5.2.3.2 Short Radius Guardrails

A second scenario that has no barrier separation and has limited approach length is shown

in Figure 24. In this case, the bridge rail ends are protected by a short radius guardrail system. The

67

Figure 23. No Barrier Separation - Limited Approach Length - Crash Cushions

68

short radius guardrail system is provided for situations where typical bridge rail end treatments

cannot be used due to the close proximity of an intersecting roadway, street, or driveway. The

guardrail section of the barrier curves around the corner and maintains a position behind the

pedestrian walkway. At this location, the guardrail is terminated by a standard guardrail end

terminal. As shown in Figure 24, the pedestrian and/or bicyclist pathways are located on the traffic-

side face of both the bridge rail and short radius guardrail system, and a curb is placed at the edge

of the traveled way. Additional discussion on the positioning of the pathways and the curbs is the

same as that provided in Section 5.2.2.1.

Finally, it should be noted that this short radius guardrail system is currently under

development and has not met the NCHRP Report No. 350 safety standards. However, it has been

included herein since it may in the future provide a viable alternative for meeting either the TL-2

or TL-3 impact safety standards.

5.2.3.3 Evaluation - No Barrier Separation, Limited Approach Length

Two methods for providing pedestrian protection on bridges where there exists limited

approach length due to an intersecting street and barrier separation is not provided have been

illustrated in Figures 23 and 24. Currently, there is not a short radius guardrail system approved to

meet the NCHRP Report No. 350 impact safety standards. As a result, an NCHRP Report No. 350-

approved crash cushion is probably the best alternative for this situation. For TL-2 applications, a

short radius guardrail system approved to the impact safety standards of NCHRP Report No. 230

may be an acceptable alternative. Again, it must be noted that placement of both crash cushions and

short radius barriers relative to curbs greatly affects their crashworthiness due to the potential for

vehicular vaulting of the barrier. Therefore, further research is required in order to determine

appropriate, safe placement of curbs near these systems.

69

Figure 24. No Barrier Separation - Limited Approach Length - Short Radius Guardrails

70

5.3 Barrier Separation Provided

Pedestrian safety on bridges is maximized when the vehicle and pedestrian lanes are

separated with either an NCHRP Report No. 350-approved bridge railing, a combination

vehicle/pedestrian bridge railing, or a combination vehicle/bicycle bridge railing (6). This physical

barrier creates positive shielding of the pedestrian lanes, thereby increasing both the actual safety

of the pedestrians as well as their perceived level of safety. At the bridge ends, an approved barrier

end treatment must be provided in order to prevent errant motorists from impacting the barrier ends

as well as to decrease the potential for vehicle snag and pocketing into a barrier system with

significant changes in lateral stiffness. However, it is noted that the barrier configuration selected

must also conform to the geometrical constraints of the bridge site without impeding the flow of the

pedestrian and/or bicycle traffic (2).

Refer to Sections 2.2.2, 2.3, and 2.5 for a comprehensive summary of the current existing

guidelines concerning the protection of pedestrians using barrier separation.

5.3.1 Unlimited Approach Length

The ideal case for designers is a bridge site with ample approach length and lateral width to

accommodate both vehicular traffic and pedestrian/bicycle safety features. In this situation,

designers can freely specify appropriate pedestrian/bicycle safety facilities as well as bridge railing

end treatments without being forced to make compromises based on geometrical site constraints.

5.3.1.1 Transitions, Guardrails, and Terminals

A scenario that has unlimited approach length and provides barrier separation is illustrated

in Figure 25. The ends of the bridge railing separating the vehicular and pedestrian/bicycle traffic

can be protected with either a TL-2, TL-3, or TL-4 approach guardrail transition, strong-post

71

guardrail, and guardrail end terminal. If a curb is present along the upstream roadway, the curb is

transitioned a swale upstream from the guardrail end terminal, as shown in Figure 26. Note that a

strong post guardrail system utilizes double blockouts and a flared end terminal to improve hydraulic

efficiency by moving the posts away from the gutter line. A swale is a roadside feature that provides

hydraulic drainage similar to that of a curb, but unlike a standard curb, it has a flat face sloping up

and away from the gutter line. Upon impact by a vehicle, this flattened face should minimize the

disruption to the vehicle’s trajectory, thereby greatly reducing the potential for vehicular instabilities

prior to reaching the guardrail. As a result, it is believed that the use of swales will eliminate the

potential for the vehicles to climb and vault over the guardrail systems.

A second scenario that has unlimited approach length, provides barrier separation, and

utilizes either a TL-2, TL-3, or TL-4 approach guardrail transition, strong-post guardrail, and

guardrail end terminal is shown in Figure 27. In this case, the curb is positioned behind the guardrail

and guardrail end terminal, as shown in Figure 28. It is desirable for the curb to be sufficiently set

back from the guardrail end terminal so that an errant vehicle will not mount the curb with the right-

front tire prior to an end-on impact with the terminal’s end. If the curb set-back distance is

sufficient, a vehicle will impact the roadside hardware prior to mounting the curb, thus eliminating

the curb’s influence on the vehicle’s trajectory during the impact sequence. In addition, this curb

configuration shifts the gutter line behind the guardrail and guardrail end terminal, thus creating

potential hydraulic problems. By forcing the gutter line to follow a path underneath and behind the

guardrail, selected posts are moved to a location in front of the curb and potentially in the path of

water runoff. Therefore, it is recommended that a water drain be placed immediately upstream of

the gutter line shift, as shown in Figure 27. Furthermore and in order to minimize the posts’ potential

72


73


74


75


76

to impede hydraulic flow, the curb and gutter line should be moved sufficiently behind the guardrail.

The combination of the sloped roadway and shifted gutter line creates a low-lying pocket which

allows water runoff to accumulate in this area. Therefore, a second water drain must also be

installed in a manner similar to that shown in Figure 27. Finally, the pedestrian and bicycle

pathways may have to be moved farther away from the guardrail and guardrail end terminal systems

in order to maintain adequate sidewalk width and continuity of the pedestrian facility.


A scenario with unlimited approach length and barrier separation provided is shown in

Figure 29. In this case, the bridge rail ends are protected with either TL-2 or TL-3 energy-absorbing

crash cushions. However, it should be noted that the manufacturer of a crash cushion device is

responsible for providing guidance for its proper application and installation. As a general rule,

crash cushions should only be used at sites which have adequate level terrain and those which are

void of curbs or other physical features that may degrade the device’s safety performance (2,6). As

shown in Figure 30, the curb was transitioned to a swale at a location upstream from the crash

cushion in order to (1) minimize the potential for vehicular instabilities prior to reaching the crash

cushion, (2) prevent climbing or vaulting over the barrier system, and (3) eliminate any restrictions

on drainage capacity. Finally, it may be necessary to move the pedestrian and bicycle pathways

farther away from the crash cushion in order to maintain adequate sidewalk width and continuity

of the pedestrian facility.

A second scenario that has unlimited approach length, provides barrier separation, and

incorporates TL-2 and TL-3 energy absorbing crash cushions is shown in Figure 31. In this case,

the curb, if present on the approach roadway, is positioned behind the crash cushion. This curb

77


78


79


80

configuration also shifts the gutter line behind the crash cushion. The combination of the sloped

roadway and shifted gutter line creates a low-lying pocket which allows water runoff to accumulate

in this area. Therefore, a water drain must be installed in a manner similar to that shown in Figure

31. It also may be necessary to move the walkway/pathway away from the crash cushion in order

to maintain adequate sidewalk width and continuity of the pedestrian facility.

5.3.1.3 Low-Height Barriers

A scenario that has unlimited approach length and provides barrier separation is shown in

Figure 32. For this situation, a low-height barrier is provided and configured with a sloped end

treatment, both of which are approved for TL-2 applications (23). Since pedestrians or bicyclists

are positioned behind this barrier system, an independent pedestrian or bicycle railing will be

required between the vehicle and pedestrian lanes. However, to date, there does not exist a

pedestrian/bicycle railing that is approved for use on or directly behind this low-height bridge

railing.

Independent pedestrian/bicycle railings are typically designed for only pedestrian/bicycle

loading. As a result, potential safety concerns exist when these railings are subjected to vehicular

impacts. For example, an impacting vehicle may dislodge structural elements from the

pedestrian/bicycle railing and cause hazardous debris to be thrown into the pedestrian or bicycle

lanes. In addition, bridge railing components could become fractured and potentially penetrate the

vehicle’s interior occupant compartment. For both of these scenarios, the pedestrians as well as the

vehicles’ occupants would be subjected to undue risk. Therefore, if this low-height bridge railing

configuration is to be utilized for this application, special consideration must be directed to both the

location and the design of the pedestrian/bicycle railing.

81

Figure 32. Barrier Separation Provided - Unlimited Approach Length - Low Height Barriers

82

Two alternatives are available to the engineers when considering the design of

pedestrian/bicycle railings for oblique vehicular impacts. First, if the pedestrian/bicycle railing is

physically attached to the low-height bridge railing, then full-scale vehicle crash testing in

accordance with the NCHRP Report No. 350 impact safety standards would be required. Second,

if the pedestrian/bicycle railing is not attached to the low-height bridge railing, then it is

recommended that the pedestrian/bicycle railing be placed behind the traffic-side face of the barrier

and outside of the zone of intrusion (ZOI). This position should be selected in order to ensure that

it will not be struck by an impacting vehicle which may extend over the top of the bridge railing.

For this second alternative, additional full-scale vehicle crash testing will not likely be required.

The ZOI for the TL-2 low-height concrete barrier is 711 mm, which is specified for all

concrete barriers shorter than 686-mm tall in the MwRSF Report entitled Guidelines for Attachments

to Bridge Rails and Median Barriers (32). If the railing is to contain pedestrians on foot, it must be

a minimum of 1,067-mm tall. For bicycle facilities, the railing must be a minimum of 1,372-mm

tall (2-3,7). The main benefits of the low-height barrier in this situation are its redirective

capabilities at the TL-2 service level and the shortened height which greatly improves visibility for

motorists. The disadvantage of this configuration is that an independent pedestrian/bicycle railing

is required between the low-height barrier and the pedestrian/bicycle pathway, likely resulting in

additional cost and complexity to the bridge structure.

Finally, the end treatment for the combination low-height and pedestrian/bicycle bridge

railing will likely require a much more complex solution. If the combination railing’s end terminal

is installed tangent to the roadway and close to the back side of the low-height barrier, as shown in

Figure 32, then a crashworthy end treatment will be required for both the low-height barrier as well

83

as the pedestrian/bicycle railing. However, if an independent pedestrian/bicycle railing is

constructed sufficiently behind the low-height barrier, then the potential exists for only requiring

that the sloped concrete end terminal be crashworthy.

5.3.1.4 Evaluation - Barrier Separation Provided, Unlimited Approach Length

Five methods for providing pedestrian protection on bridges where unlimited approach

length exists at the end of the bridge and barrier separation is provided have been illustrated in

Figures 25 through 32. If the bridge rail end is to be protected by transitions, guardrails, and

guardrail end terminals, the first configuration shown in Figures 25 and 26 is the most suitable in

terms of crashworthiness, pedestrian safety, and hydraulic efficiency. A swale, used in lieu of a

standard curb, minimizes the potential for vehicular instabilities while providing adequate hydraulic

drainage capacity. A second application using transitions, guardrails, and guardrail end terminals

is shown in Figures 27 and 28. However, it should be noted that this case will likely be more costly

than the first application due to the additional considerations deemed necessary in order to maintain

adequate drainage. Crash cushions are the second option to be considered for the termination of

bridge rail ends, as well as for the protection of pedestrians and bicyclists. Once again, as shown

in Figures 29 and 30, a swale is placed underneath a crash cushion in order to minimize the potential

for vehicular instabilities while providing adequate hydraulic drainage capacity. The crash cushion

configurations depicted in Figures 29 and 31 are equivalent in terms of their crashworthiness.

However, the curb alternative may not be preferred over the swale alternative due to the perceived

higher construction costs and additional water inlet requirements. Finally, the low-height barrier

with a pedestrian/bicycle railing, as illustrated in Figure 32, can be used to provide adequate

pedestrian protection over bridges. However, there currently is not an NCHRP Report No. 350-

84

approved pedestrian/bicycle railing developed for use with the low-height barrier.

5.3.2 Limited Approach Length

Bridge sites with limited approach length will not allow the use of conventional approach

guardrail transitions, standard guardrail, and guardrail end terminals. In these situations, the

designer is forced to specify alternative bridge rail end treatments that are appropriate to satisfy the

safety requirements of the site.


A scenario that provides barrier separation and has limited approach length is shown in

Figure 33. In this case, the bridge rail ends are protected with either a TL-2 or TL-3 energy-

absorbing crash cushion. A crash cushion is used in place of approach guardrail transitions, standard

guardrails, and guardrail end terminals due to the close proximity of the intersecting roadway, street,

or driveway on the approach side of the bridge. If a curb is required for drainage control, it should

be positioned behind the crash cushion in order to maintain the crashworthiness of the device.

Finally, it also may be necessary to move the pedestrian and bicycle pathways farther away from the

crash cushion in order to maintain adequate sidewalk width and continuity of the pedestrian facility.

5.3.2.2 Low-Height Barriers

A scenario that provides barrier separation and has limited approach length is shown in

Figure 34. For this situation, a low-height barrier is once again provided and configured with a

sloped end treatment, both of which are approved for TL-2 applications (23). For this example, a

curb is provided for drainage control at the edge of the roadway and smoothly transitions to the

shape of the upstream end of the sloped concrete end terminal.

One of the situations for which the low-height bridge rail was developed was for the

85

accommodation of pedestrians or bicyclists when site restrictions prevent the use of conventional

bridge rails, approach guardrail transitions, and guardrail end terminals. Since pedestrians or

bicyclists are positioned behind this barrier system, an independent pedestrian or bicycle railing will

be required between the vehicle and pedestrian lanes. However, to date, there does not exist a

pedestrian/bicycle railing that is approved for use on or directly behind this low-height bridge

railing. Additional discussion on the design, location, and crashworthiness of the pedestrian and

bicycle railing system is the same as that provided previously in Section 5.3.1.3.

The ZOI for the TL-2 low-height concrete barrier is 711 mm, which is specified for all

concrete barriers shorter than 686-mm tall in the MwRSF Report entitled Guidelines for Attachments

to Bridge Rails and Median Barriers (32). If the railing is to contain pedestrians on foot, it must be

a minimum of 1,067-mm tall. For bicycle facilities, the railing must be a minimum of 1,372-mm

tall (2-3,7). The main benefit of the low-height barrier in this situation is minimal length required

to terminate the barrier. The low-height barrier also provides redirective capabilities at the TL-2

service level, and the shortened height greatly improves driver visibility. The disadvantage of this

configuration is that an independent pedestrian/bicycle railing is required between the low-height

barrier and the pedestrian and bicycle pathways, likely resulting in additional cost and complexity

to the bridge structure.

5.3.2.3 Short Radius Guardrails

A third scenario that provides barrier separation and has limited approach length Figure 35.

In this case, the bridge rail ends are protected by a short radius guardrail system. A short radius

guardrail system is provided for situations where typical bridge rail end treatments cannot be used

due to the close proximity of an intersecting roadway, street, or driveway. The guardrail section of

86

Figure 33. Barrier Separation Provided - Limited Approach Length - Crash Cushions

87

Figure 34. Barrier Separation Provided - Limited Approach Length - Low Height Barriers

88

Figure 35. Barrier Separation Provided - Limited Approach Length - Short Radius Guardrails

89

the barrier curves around the corner and maintains a position between the pedestrian walkway and

the traffic lanes. At this location, the guardrail is terminated by a standard guardrail end terminal.

A pedestrian crossing is then provided at the end of the guardrail terminal.

If a curb is utilized, it must be moved laterally away from the vehicle lanes and placed

behind the guardrail system. As shown in Figure 36, the standard curb is transitioned to a section

having a flattened face sloping upward and away from the gutter line and at a location directly

behind the elbow of the short radius system. If a vehicle impacts the nose section of the short radius

guardrail system, the vehicle’s front end should be adequately captured prior to the vehicle’s front

wheels traversing over the curb. Subsequently, the vehicle will continue to penetrate into the barrier

system and then will be brought to a controlled stop. This behavior will be best achieved with the

use of a flattened slope measuring no greater than 10:1.

Finally, it should be noted that this short radius guardrail system is currently under

development and has not met the NCHRP Report No. 350 safety standards. However, it has been

included herein since it may in the future provide a viable alternative for meeting either the TL-2

or TL-3 impact safety standards.

5.3.2.4 Evaluation - Barrier Separation Provided, Limited Approach Length

Three methods for providing pedestrian protection on bridges where there exists limited

approach length due to an intersecting street, and barrier separation is provided have been

illustreated in Figures 33 through 36. Of these three configurations, an NCHRP Report No. 350-

approved crash cushion is the most viable means for terminating the bridge rail ends and for

protecting pedestrians and bicyclists, as illustrated in Figure 33. Currently, a short radius guardrail

system has not met the NCHRP Report No. 350 impact safety standards. However, a short radius

90

guardrail system crash tested according to the NCHRP Report No. 230 criteria may be an acceptable

alternative for use in TL-2 applications. Finally, the low-height barrier with a pedestrian/bicycle

railing, as illustrated in Figure 35, can be used to provide adequate pedestrian protection over

bridges. However, currently there is not an NCHRP Report No. 350-approved pedestrian/bicycle

railing developed for use with the low-height barrier.

91

Figure 36. Barrier Separation Provided - Limited Approach Length - Short Radius Guardrails

92

6 SUMMARY AND CONCLUSIONS

The objectives of this study were to identify the most common scenarios in which the

protection of pedestrians on bridges is desirable and then develop bridge rail and bridge rail end

treatment configurations to accommodate those situations. The first study objective was achieved

by performing a field investigation, a survey of state transportation agencies, and an extensive

literature review. The field investigation and state survey resulted in the identification of the most

common situations where pedestrian protection is desired. The literature review identified roadside

hardware available, or currently under development, for use in providing improved pedestrian

protection on or near the ends of bridges. Recommendations for the placement and design of

standard barrier configurations have been provided in the form of generalized site drawings. The

barrier configurations were developed and organized using two main criteria: (1) the presence or

absence of a physical barrier separating the vehicle and pedestrian lanes and (2) the amount of

available approach length upstream from the bridge rail ends.

It was impractical and unnecessary to conduct full-scale vehicle crash tests for all of the

recommended barrier configurations. Instead, the barrier configurations outlined within this report

were based on NCHRP Report No. 350-approved hardware, roadside hardware meeting prior safety

standards, hardware believed to provide moderate safety, hardware currently under development,

and sound engineering judgement. Therefore, it is noted that the barrier configurations

recommended herein are not equivalent in terms of the level of pedestrian safety provided. As a

result, sound engineering judgement is required when determining which barrier configuration to

implement.

Although this report outlines some suitable barrier configurations for use in the protection

93

of pedestrians on bridges, the information upon which the recommendations were developed is by

no means complete. The barrier configurations illustrated herein were developed based upon the

limited data and general guidelines that are currently available. Therefore, it should be recognized

that the final product is limited to a similar degree. In that regard, it is concluded that additional

research studies and crash testing programs that yield objective results would greatly enhance the

present state of knowledge from which these engineering judgements were based. Obtaining more

objective data would undoubtedly expand the scope of the solutions presented herein, and ultimately

improve the safety of pedestrian facilities on and near the ends of bridges.

94

7 RECOMMENDATIONS

In a future study, an objective methodology should be established for roadway and bridge

engineers to utilize when assessing the need for pedestrian protection as well as to assist in

adequately and consistently specifying pedestrian safety facilities on and near the ends of bridges

and under various traffic conditions. Development of such an objective methodology will likely be

achieved by using the RSAP benefit-to-cost ratio analysis program, resulting in general guidelines

that can be applied to most roadside situations. The barrier configurations developed within this

report should be evaluated using this objective methodology in order to rank and determine which

alternatives provide the greatest pedestrian safety for a given site. The existence of objective

assessment and specification techniques for use by engineers and designers will lead to safer

pedestrian facilities on or near the ends of bridges.

Curbs, used in conjunction with roadside barriers, is another area where further research is

required in order to improve the safety of pedestrian facilities on or near bridges. Currently,

engineers and designers have very limited guidance when the placement of roadside barriers behind

or above curbs is required. Research studies involving computer simulation modeling and full-scale

vehicle crash testing should continue in order to investigate vehicle behaviors during impacts with

curb/barrier combinations. The results will provide knowledge and insight with which objective

guidelines can later be developed.

There is a need for new TL-2 and TL-3 bridge railing end treatments that can accommodate

bridge sites with limited approach length beyond the bridge end. The short radius guardrail system

is a natural solution to this problem. However, a short radius guardrail system has not met the TL-2

or TL-3 safety standards found in NCHRP Report No. 350. Therefore, it is apparent that the

95

development and approval of a short radius guardrail system for use in these situations would greatly

benefit the safe accommodation of pedestrians on and near the ends of bridges.

Finally, increased pedestrian safety on or near bridges could be provided with the continued

development of crashworthy vehicle/pedestrian and vehicle/bicycle railings. As discussed in Section

2.6.3, only a few NCHRP Report No. 350-approved vehicle/pedestrian and vehicle/bicycle railings

are available for use where no barrier separation is provided, and even fewer crashworthy systems

are available for situations where barrier separation is provided. With physical barrier separation

being the most common and most effective method to separate vehicles and pedestrians, it is

apparent that the specification of more crashworthy combination bridge railings would enhance the

safety of pedestrians on bridges.

96

8 REFERENCES

1. Ross, H.E., Sicking, D.L., Zimmer, R.A. and Michie, J.D., Recommended Procedures forthe Safety Performance Evaluation of Highway Features, National Cooperative HighwayResearch Program (NCHRP) Report No. 350, Transportation Research Board, Washington,D.C., 1993.

2. A Policy on Geometric Design of Highways and Streets, American Association of StateHighway and Transportation Officials (AASHTO), Washington, D.C., 2001.

3. AASHTO LRFD Bridge Design Specifications, Customary U.S. Units – First Edition,American Association of State Highway and Transportation Officials (AASHTO), 2001Interim.

4. Guide for the Development of Bicycle Facilities, American Association of State Highwayand Transportation Officials (AASHTO), Washington, D.C., 1999.

5. Wilkinson, W.C., III, Clarke, A., Epperson, B., Knoblauch, R., Selecting Roadway DesignTreatments to Accommodate Bicycles, Report No. FHWA-RD-92-073, Submitted to theOffice of Safety and Traffic Operations, Federal Highway Administration, Performed byCenter for Applied Research, Inc., January 1994.

6. Roadside Design Guide, American Association of State Highway and TransportationOfficials (AASHTO), Washington, D.C., 2002.

7. Standard Specifications for Highway Bridges, 15th Edition, American Association of StateHighway and Transportation Officials (AASHTO), Washington, D.C., 1992.

8. Olson, R.M., Weaver, G.D., Ross, H.E. Jr., and Post, E.R., Effect of Curb Geometry andLocation on Vehicle Behavior, NCHRP Report 150, 1974.

9. Ray, M.H., Plaxico, C.A., Recommended Guidelines for Curbs and Curb-BarrierCombinations, NCHRP Interim Report 22-17, October, 2000.

10. Faller, R.K., Reid, J.D., Rohde, J.R., Sicking, D.L., Keller, E.A., Two Approach GuardrailTransitions for Concrete Safety Shape Barriers, Final Report to the Midwest State’sRegional Pooled Fund Program, Transportation Record No. TRP-03-69-98, MidwestRoadside Safety Facility, University of Nebraska-Lincoln, May 15, 1998.

11. Faller, R.K., Reid, J.D., Rohde, J.R., Two Approach Guardrail Transitions for ConcreteSafety Shape Barriers, Transportation Record No. 1647, Transportation Research Board,National Research Council, 1998, pp 111-121.

97

12. Buth, C.E., Menges, W.L., Schoeneman, S.K., Roadside Safety Hardware Tested inAccordance With NCHRP Report 350, Report No. 404201-F, Texas Transportation Institute,Texas A&M University, College Station, Texas, February 2001, pp 5-22.

13. Polivka, K.A., Faller, R.K., Sicking, D.L., Rohde, J.R., Reid, J.D., and Holloway, J.C.,Guardrail and Guardrail Terminals Installed Over Curbs, Final Report to the MidwestState’s Regional Pooled Fund Program, Transportation Record No. TRP-03-83-99, MidwestRoadside Safety Facility, University of Nebraska-Lincoln, March 21, 2000.

14. Polivka, K.A., Faller, R.K., Sicking, D.L., Rohde, J.R., Reid, J.D., and Holloway, J.C.,Guardrail and Guardrail Terminals Installed Over Curbs – Phase II, Final Report to theMidwest State’s Regional Pooled Fund Program, Transportation Record No. TRP-03-105-00, Midwest Roadside Safety Facility, University of Nebraska-Lincoln, November 5, 2001.

15. Polivka, K.A., Faller, R.K., Sicking, D.L., Rohde, J.R., Reid, J.D., and Holloway, J.C.,Design & Evaluation of the TL-4 Minnesota Combination Traffic/Bicycle Bridge Rail, FinalReport to the Midwest State’s Regional Pooled Fund Program, Transportation Record No.TRP-03-109-01, Midwest Roadside Safety Facility, University of Nebraska-Lincoln,September 5, 2001.

16. Bullard, D.L., Jr., Menges, W.L., Buth, C.E., Development of Combination Pedestrian-Traffic Bridge Railings, Transportation Research Record No. 1468, Transportation ResearchBoard, National Research Council, 1994, pp 41-53.

17. Guide Specifications for Bridge Railings, American Association of State Highway andTransportation Officials (AASHTO), Washington, D.C., 1989.

18. Hirsch, T.J., Buth, C.E., Aesthetically Pleasing Combination Pedestrian-Traffic Bridge Rail,Transportation Research Record No. 1367, Transportation Research Board, NationalResearch Council, 1992, pp 23-35.

19. Kimball, C.E., Mayer, J.B., Full-Scale Crash Evaluation of the NETC 4-Bar Sidewalk-Mounted Steel Bridge Railing, Report No. FHWA-RD-99-027, Submitted to the Office ofContracts and Procurement, Federal Highway Administration, Performed by SouthwestResearch Institute, 1998.

20. Guidry, T.R., Beason, W.L, Development of a Low-Profile Portable Concrete Barrier,Transportation Research Record No. 1367, Transportation Research Board, NationalResearch Council, 1992, pp 36-46.

21. Guidry, T.R., Beason, W.L, Development of a Low-Profile Portable Concrete Barrier,Research Report No. 990-4F, Texas Transportation Institute, Texas A&M University,College Station, Texas, November 1991.

98

22. Beason, W.L., Menges, W.L., and Ivey, D.L., Compliance Testing of an End Treatment forthe Low-Profile Concrete Barrier, Research Report No. 1403-S, Texas TransportationInstitute, Texas A&M University, College Station, Texas, April 1998.

23. Polivka, K.A., Faller, R.K., Sicking, D.L., Rohde, J.R., Reid, J.D., and Holloway, J.C.,Development of a Low Profile Bridge Rail for Test Level 2 Applications, Final Report to theMidwest State’s Regional Pooled Fund Program, Transportation Record No. TRP-03-109-02, Midwest Roadside Safety Facility, University of Nebraska-Lincoln, August 20, 2002.

24. Consolazia, G.R., Chung, J.H., Gurley, K.R., Development of a Low Profile Work ZoneBarrier Using Impact Finite Element Simulation, Presented at the 2002 Annual Meeting ofthe Transportation Research Board, Washington, D.C., January 2002.

25. Kansas Department of Transportation, Design Manual, Volume III, Version 9/01, BridgeSection, Metric.

26. Missouri Department of Transportation, Project Development Manual, Chapter IV, Revised4/1/02, Available: <http://www.modot.state.mo.us/design/ppdm/ppdm.htm> [2002, June 4].

27. Minnesota Department of Transportation, Bridge Design Manual, July 1998.

28. South Dakota Department of Transportation, Road Design Manual, Available:<http://www.sddot.com/pe/roaddesign/plans_rdmanual.asp> [2002, June 4].

29. Texas Department of Transportation, Bridge Railing Manual, Revised February 2002,Available: <http://manuals.dot.state.tx.us/dynaweb/colbridg/rlg/@Generic__BookView >[2002, June 4].

30. Texas Department of Transportation, Roadway Design Manual, Revised April 2002,Available: <http://manuals.dot.state.tx.us/dynaweb/coldesig/rdw/@Generic__BookView>[2002, June 4].

31. Michie, J.D., Recommended Procedures for the Safety Performance Evaluation of HighwayAppurtenances, National Cooperative Highway Research Program (NCHRP) Report No.230, Transportation Research Board, Washington, D.C., March 1981.

32. Keller, E.A., Sicking, D.L., Faller, R.K., Polivka, K.A., Rohde, J.R., Guidelines forAttachments to Bridge Rails and Median Barriers, Draft Report to the Midwest State’sRegional Pooled Fund Program, Transportation Record No. TRP-03-98-01, MidwestRoadside Safety Facility, University of Nebraska-Lincoln, April 13, 2001.

bridge rails and transitions for pedestrian protection · barrier configuration to implement for...

Documents